Vibratory motors and methods of making and using same

ABSTRACT

A single piezoelectric is excited at a first frequency to cause two vibration modes in a resonator producing a first elliptical motion in a first direction at a selected contacting portion of the resonator that is placed in frictional engagement with a driven element to move the driven element in a first direction. A second frequency excites the same piezoelectric to cause two vibration modes of the resonator producing a second elliptical motion in a second direction at the selected contacting portion to move the driven element in a second direction. The piezoelectric is preloaded in compression by the resonator. Walls of the resonator are stressed past their yield point to maintain the preload. Specially shaped ends on the piezoelectric help preloading. The piezoelectric can send or receive vibratory signals through the driven element to or from sensors to determine the position of the driven element relative to the piezoelectric element or resonator. Conversely, the piezoelectric element can receive vibration or electrical signals passed through the driven element to determine the position of the driven element. The resonator is resiliently urged against the driven element, or vice versa. Plural resonators can drive common driven elements.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. §119(e) fromU.S. patent application Ser. No. 60/191,876 filed Mar. 23, 2000 entitled“Electric Motor Using Vibration to Convert Electrical Energy IntoMechanical Motion” and listing inventors Bjoern Magnussen, SteveSchofield and Ben Hagemann; and from application Ser. No. 60/215,438filed Jun. 30, 2000, application Ser. No. 60/215,686 filed Jun. 30,2000, application Ser. No. 60/231,001 filed Sep. 8, 2000, andapplication Ser. No. 60/236,005 filed Sep. 27, 2000; each entitled“Electrical Motor Using Vibration to Convert Electrical Energy IntoMechanical Motion” and listing inventors Bjoern Magnussen, Ben Hagemannand Peter Varadi. The entire disclosures of these preceding applicationsare incorporated by this reference as though set forth fully herein.

BACKGROUND OF THE INVENTION

[0002] To move small components, electromagnetic motors are often usedbecause they are relatively inexpensive. The electromagnetic motorsrotate very quickly and can only apply a low force, so they are alwaysused with a gearbox that provides the slower motion and increased powernecessary for practical applications. It should be noted that themovement of driven elements referred to in this disclosure refers to atranslation or rotary motion in a common direction, and does notincluded motion that merely moves a part alternatively back and forth toshake the part without any net movement. While the conventionalelectromagnetic motors are relatively inexpensive, there are a largenumber of moving parts which complicates assembly and reliability, andthe low power and need for a gearbox not only limits their applicationbut also makes the cost excessive for many applications. Moreover, thesemotors are too big, not very precise in their motion, and are noisy.There is thus a need for a simpler, quieter and less expensive motor.

[0003] An alternative type of small motor is a piezoelectric motor,which uses a material that can change dimension when a voltage isapplied to the material. Piezoelectric ceramics are used inelectromechanical micromotors to provide linear or circular motion bymaking frictional contact between the vibratory motor and a drivenobject. These piezoelectric motors are composed of at least onemechanical resonator and at least one piezoelectric actuator. Whenelectrically excited by oscillating electrical signals, the actuatorgenerates mechanical vibrations that are amplified by the resonator.When the resonator is brought into contact with a body, these vibrationsgenerate frictional forces in the contact area with the body and causethe body to move. The speed, direction and mechanical power of theresulting mechanical output depend on the form and frequency of thevibrations in the contact area. These piezoelectric motors work withsmall changes in dimension for a given voltage, and they can vibrate atmany tens of thousands of cycles per second. Various cumbersome andexpensive designs have been used to obtain useful forces and motionsfrom these small vibratory motions.

[0004] One type of piezoelectric motor is a traveling wave motor, whichuses a wave that travels through the piezoelectric material. Thesemotors typically are based on a disc shaped design and are expensive toproduce. The shape and the cost of these motors limit their application.

[0005] Other types of piezoelectric motors require a specially shapedwaveform in the input signal in order to cause the piezoelectricmaterial to move in a desired direction. One such type of motor isreferred to as a stick-slip drive. These motors have a piezoelectricelement that moves an object in a desired direction on a support at arelatively slow rate sufficient to allow friction to move the object.The waveform applied to the piezoelectric element causes thepiezoelectric to then quickly retract and effectively pull the supportout from under the object causing the object to slip relative to thesupport. The process is repeated, resulting in motion. Since thesemotors require a sawtooth or similar shaped waveform to operate, theyrequire complex electronics that increase the cost of such motors.

[0006] A yet further type of piezoelectric motor is the impact drive,which repeatedly hits an object in order to make it move.

[0007] In piezoelectric micromotors, the piezoelectric element can beused to excite two independent modes of vibration in the resonator. Eachmode causes the contact area on the resonator to oscillate along acertain direction. The modes are often selected so that the respectivedirections of oscillation are perpendicular to each other. Thesuperposition of the two perpendicular vibrations cause the contact areato move along curves known as Lissajous figures. For example, if bothvibrations have the same frequency and no relative phase shift betweenthe vibrations, the motion resulting from the superposition is linear.If the frequencies are the same and the relative phase shift is 90degrees, then the resulting motion is circular if the amplitudes of eachvibration are identical; otherwise the resulting motion is elliptical.If the frequencies are different, then other motions such asfigure-eights can be achieved.

[0008] The Lissajous figures have been used to produce figure-eightmotion drives. These drives require an electrical signal that has tocontain two frequencies to cause a tip of the vibration element to movein a figure-eight shaped motion. The resulting electronics are complexand expensive, and it is difficult to use the figure-eight motion tocreate useful motion of an object.

[0009] In order to move another body and to create a mechanical output,circular or large-angle elliptical motions (semi-axes nearly equal) havebeen preferred over linear motions. Piezoelectric micromotors in theprior art thus commonly employ two perpendicular modes of vibration thathave a relative phase shift of approximately ninety degrees. The modesare excited close to their respective resonance frequencies so that theresulting mechanical output is maximized. If the relative phase shiftbetween the two modes is changed to −90 degrees, the direction in whichthe ellipse is traversed is reversed. The motion of the body in contactwith the resonator is thus reversed as well. But these conventionalmotors require two piezoelectric drivers located and selected to excitethe two separate resonant modes. This requires two sets of drivers, twosets of electronic driving systems, an electronic system that willreverse the phase of each driver, and the basic design placeslimitations on the locations of components.

[0010] The prior art thus includes electromechanical micromotors where arod-like resonator has a small piezoelectric plate that is attached tothe resonator. The resonator contacts the moving body at the tip of therod. The actuator excites a longitudinal mode and a bending mode of therod. The excitation frequency is chosen in-between the two resonancefrequencies of the respective modes so that the relative phase shift is90 degrees. The phase shift is generated by the mechanical properties ofthe resonator, in particular its mechanical damping properties. Theresulting elliptical motion of the resonator's tip is such that one ofthe semi-axes of the ellipse is aligned with the rod-axis and the othersemi-axis of the ellipse is perpendicular thereto. A secondpiezoelectric actuator is used to reverse the direction in which theellipse is traversed, and is placed at a different location on theresonator. The second piezoelectric actuator is located in such a waythat it excites the same two modes but with a relative phase shift of−90 degrees.

[0011] Unfortunately, this actuator requires two sets of electronics todrive the motor in opposing directions, and has two sets of drivingpiezoelectric plates, resulting not only in a large number of parts butalso greatly increasing the complexity of the system and resulting insignificant costs for these type of motors. The motor also has limitedpower because the driving frequency is selected to be between tworesonant frequencies. There is thus a need for a vibratory motor withsimpler electronics, fewer parts, and greater efficiency.

[0012] In other vibratory motors, a piezoelectric element has a numberof electrodes placed on different portions of the element in order todistort the element in various ways. Thus, for example, two modes ofvibration can be excited by at least two separate, independently excitedelectrodes in each of four quadrants of a rectangular piezoelectricceramic element. A second set of electrodes is used to reverse thedirection in which the ellipse is traversed. The resulting ellipticalmotion is such that one of the semi-axes of the ellipse is aligned withthe longitudinal axis of the motor and the other semi-axes of theellipse is perpendicular thereto. As mentioned elsewhere, the ratio ofthe semi-axes can be advantageously used to increase motion or reducetravel time, by making advantageous use of ratios of 5:1, 10:1, or from20-50:1. Again though, there are a number of electronic connections andmany parts to achieve this motion, resulting in a high cost for thistype of motor. It is an object of some aspects of the present inventionto provide a micromotor, which is cheaper and easier to manufacture thanprevious art.

SUMMARY OF THE INVENTION

[0013] This invention uses a single piezoelectric element and amechanical resonator to achieve its desired motion. The piezoelectricelement has one pair of electrical contacts. The piezoelectric elementis excited using sinusoidal electrical signals with the element,resonator, and sometimes the mounting system being configured so that atleast two modes of vibration are excited by the single signal togenerate an elliptic motion in the area where the resonator comes intocontact with the body to be moved.

[0014] Unlike the prior art, the semi-axes of the ellipse advantageouslyare neither aligned with the longitudinal axis of the resonator nor in adirection perpendicular to it. Also, the relative phase shift betweenthe two modes need not be close to 90 degrees so as to produce acircular or nearly circular-elliptical path. The amplitudes of therespective vibrations can be different in magnitude. At a givenfrequency, the motor 26 (see FIG. 1) moves the body 42 in one direction.When operated at a different frequency, the motor 26 moves the body 42in a different direction or different rotation. Preferably, it moves thebody 42 in the opposite direction, but this will depend on the needs ofthe user and the design of the motor 26, its support, and the drivenbody 42. It is possible to operate the motor 26 at even more frequenciesto generate additional motions of the body such as rotation and/ortranslation of an axle. The movement of driven body 42 in thisdisclosure refers to a translation or rotary motion of the body 42 in acommon direction, rather than motion that merely moves the body 42alternatively back and forth in a cyclic path to shake the body withoutany net translation or net rotation.

[0015] According to the invention, a piezoelectric element is mountedinside a mechanical resonator in part to preload the element incompression. The combined piezoelectric element and mechanical resonatorare referred to as a motor or as a vibration element. The combinedpiezoelectric element and resonator are configured so that a singledriving frequency excites at least two vibration modes sufficiently tocause an elliptical motion in a first direction at a predetermined pointon the motor that is going to be used to drive a driven object. Inparticular, a vibration mode is typically along the longitudinal axis ofthe motor, and a second vibration mode is transverse thereto so as toresult in bending or torsion. The motion can be achieved byappropriately configuring the resonator and piezoelectric element, or insome cases by locating the driving piezoelectric element offset from alongitudinal axis of the resonator to cause combined axial and bendingmotion.

[0016] The motion at a distal edge 44 at a distal end 36 of theresonator is typically greatest and is preferably used, although otherlocations on the motor can be used in some specific embodiments. Theopposing end of the motor is the proximal end 35. The result is thedistal edge moves in an elliptical path resulting from a combination ofat least two vibration modes when the motor is excited by a singlesignal at a first frequency. The motor is further configured such that asecond driving frequency excites two resonant vibration modes in themotor so that the predetermined point on the motor rotates in anelliptical path in an opposite direction as the first elliptical path. Asingle piezoelectric element and resonator are thus driven by a singlefrequency to generate a first elliptical motion at a predeterminedlocation on the vibratory motor. The piezoelectric element is driven ata second frequency to excite two resonant vibration modes of thevibratory motor that cause the predetermined location to move in asecond elliptical motion in a different, and preferably oppositedirection to the first elliptical motion, sufficient to move the drivenelement a desired distance. The two elliptical motions are typically notoverlapping. The motion can be achieved at various locations on themotor, in varying amplitudes and directions, and that allows a varietyof arrangements in which the motor can drive other elements.

[0017] In accordance with the invention, the motor thus requires asingle piezoelectric driver, a single resonator, and two separatefrequencies to move objects in two opposing directions. The selectionand configuration of the piezoelectric driver and the resonator achieveresonance or near resonant vibrations of sufficient magnitude to moveobjects with predetermined force. The effort expended in the designresults in a motor of simple design, few parts, low cost and highefficiency.

[0018] In a further embodiment, the motor is resiliently urged towardthe driven object. Depending on the mounting arrangement, the mountingmay become part of the vibrating mass and affect the resonant vibrationmodes of the motor in order to achieve the desired motion at the desiredlocation on the motor that is to be in contact with the driven object.

[0019] A simplified vibratory system is provided that has a source ofvibration in driving communication with a resonator that has a selectedcontacting portion located to engage the driven element during use ofthe system. The source of vibration is preferably a piezoelectricelement, but could comprise other elements that convert electricalenergy into physical motion, such as magnetostrictive orelectrostrictive devices in some specific embodiments. For convenience,a piezoelectric vibration source will usually be used in thisdescription.

[0020] The vibrating element and resonator are configured to move theselected contacting portion in a first elliptical motion when theresonator is excited to simultaneously resonate in at least twovibration modes by a first signal at a first frequency provided to thevibrating element, according to a specific embodiment. The resultingelliptical motion is of sufficient amplitude to move the driven elementwhen the driven element and selected contacting portion are maintainedin sufficient contact to achieve movement of the driven element. The atleast two vibration modes are selected so that at least one does notinclude a pure longitudinal or bending mode of the resonator in order toproduce the first elliptical motion. The movement of driven elementsreferred to in this disclosure refers to a translation or rotary motionin a common direction, rather than motion that merely moves a partalternatively back and forth to shake the part without any nettranslation or net rotation.

[0021] The piezoelectric element and resonator are preferably configuredto cause the selected contacting portion to move in a second ellipticalmotion a desired amount when excited to simultaneously resonate in atleast two vibration modes by a second signal at a second frequencyprovided to the piezoelectric element, according to the specificembodiment. This allows multi-degree motion of the driven element by asingle vibrating element. Additional vibration modes excited bydifferent discrete frequencies can be used to provide different motionsto the same selected contacting portion, or to different selectedcontacting portions engaging different driven elements. In one versionof a preferred embodiment, the resonator comprises an elongated memberwith the selected contacting portion being located on an edge of adistal end of the member.

[0022] A number of variations on this basic combination are described,after which some further features and advantages are discussed. Onevariation includes having a resilient element interposed between a baseand the vibratory element and located to resiliently urge the vibratoryelement against the driven element during operation of the system. Thereare advantages to having the vibration mode produce a node on theresonator element at the first frequency, with a resilient mountingconnected to the vibratory element at the node and located toresiliently urge the vibratory element against the driven element duringoperation of the system. The resilient mounting could also be connectedto the vibratory element at a location other than the node yet stilllocated to resiliently urge the vibratory element against the drivenelement during operation of the system. The resilient mounting can helpdetermine the various vibration modes.

[0023] Advantageously, the piezoelectric element is held in compressionin the resonator during operation of the system. Preferably, thepiezoelectric element is press-fit into an opening in the resonator toplace the piezoelectric element in compression during operation of thesystem. Further advantages of this press-fit can be achieved if thepiezoelectric element is held in compression by walls of the resonatorthat are stressed past their yield point, during operation of thesystem. Further advantages are derived by having the walls curved.Advantages are also provided if the piezoelectric element has aninclined surface adjacent an edge of the piezoelectric element to makeit easier to press-fit the piezoelectric element into an opening in theresonator.

[0024] The first and second elliptical motions each have a major andminor axis, and there are advantages to having the ratio of the major tominor axes of each elliptical motion being in the range of about 3:1 to150:1, and preferably from about 4:1 to 30:1, and ideally from about 5:1to 15:1. Among other advantages, faster motion can be achieved, and thesystem design is easier to achieve. Advantageously, one of the major orminor axes is aligned with an axis of motion of the driven element inorder to maximize the motion, and preferably the major axis is aligned.

[0025] There are advantages to having the major axes of these ellipsesinclined at an angle with respect to a predominant axis of the vibratoryelement, and to maintain that inclination angle over a range of drivingfrequencies. There are thus advantages to having the systemconfiguration and angle of inclination selected so that an angle βbetween the major axis and a tangent to the driven element at theselected contacting portion and along the direction of motion, varies byabout 25 degrees or less over a frequency range of about 200 Hz orgreater, on either side of the first frequency. Advantageously the angleβ varies by about 10 degrees or less.

[0026] There are also advantages to having the angle vary in order toallow greater ease in system design and to improve performance, amongother factors. Thus, there are advantages to having a major axis of theelliptical motion inclined at an angle β, with the angle β being betweenabout 5-85 degrees when the selected contacting portion is drivinglyengaging the driven element. Most of these ranges omit the range whenthe angle β is between about 0-5 degrees, and that occurs when the sameselected contacting portion is used for multiple motions. But when theselected contacting portion achieves only one direction of motion of thedriven element, it is possible to more closely align the axes andachieve alignments within about 0-5 degrees of the driven motion.

[0027] Another feature of this invention is the ability to achieve thedesired motion over a range of driving frequencies in a manner thatallows the use of components with lower tolerances and thus lower costs.Thus there is provided a vibratory element having a source of vibrationvibrating a resonator to amplify the vibration. The resonator has aselected contacting portion located to engage a driven element to movethe driven element along a driven path during use of the vibratoryelement. The selected contacting portion moves in a first ellipticalpath when the source of vibration is excited by a first electricalsignal at a first frequency. The elliptical path has a major and minoraxis which are not aligned with a predominant axis of the vibratingelement by a defined angle that varies by less than about 10 degreeswhen the first frequency varies by about 200 Hz or more on either sideof the first frequency. Preferably the defined angles varies by lessthan 5 degrees when the first frequency varies by 200 Hz, and desirablywhen the first frequency varies by 2.5 kHz, or more.

[0028] The other features of this invention can also be used with thisrange of driving frequencies. Thus, as before, the source of vibrationis preferably a piezoelectric element, but other elements could be used.The motion can be caused by pure vibration modes or by at least twovibration modes that are superimposed, but preferably at least one ofthe vibration modes is not a pure longitudinal mode or pure bendingmode. Advantageously the vibratory element is connected to a resilientsupport located to resiliently urge the selected contacting portionagainst a driven element during use of the vibratory element. Asdesired, the resilient support can be used to help define the vibrationmodes generating the elliptical motion.

[0029] Another aspect of this invention comprises a vibratory componentfor moving a driven element using off-resonance vibration modes. Thevibratory component includes a vibratory element, such as apiezoelectric vibration source, mounted to a resonator to form avibrating element. The vibrating element has a selected contactingportion located to engage the driven element during use. A variety ofpiezoelectric vibration sources can be used, including pluralpiezoelectric elements to achieve the desired elliptical motion of theselected contacting portion. But preferably the selected contactingportion moving in a first elliptical path has a major axis and minoraxis when the vibration source is excited by a first electrical signalthat causes at least two vibration modes superimposed to create thefirst elliptical path. Advantageously at least one of the vibrationmodes is other than a pure longitudinal mode and other than a purebending mode. Further, for this particular aspect, at least one of theat least two vibration modes is off-resonance with the first electricalsignal being amplified sufficiently to cause the at least oneoff-resonance vibration mode to produce a motion of the selectedcontacting portion having sufficient amplitude that the resultingelliptical path can move the driven element during use. Thisoff-resonance feature can be used with other features described herein,including the resilient support, press-fit piezoelectric elements, andother features to name a few.

[0030] One feature not mentioned earlier but applicable to the variousembodiments and features of this invention is the use of a large aspectratio on the elliptical motion of the selected contacting portion. Theratio of the major axis to the minor axis is preferably about 5:1 orgreater, with ratios of 15:1 and 30:1 believed to provide usable butprogressively less desirable motion. As the aspect ratio increases, thedriving motion become more akin to an impact drive. Nevertheless, it isbelieved possible to have aspect ratios of 3:1-150:1, or even more,provide usable motion using the various features and embodiments of thisdisclosure.

[0031] One further aspect of this invention is the use of vibrationmodes other than pure longitudinal or pure bending. Thus, the inventionincludes a vibration source mounted to a resonator to form a vibratingelement. The vibrating element has a selected contacting portion locatedto engage the driven element during use. The selected contacting portionmoves in a first elliptical path having a major axis and minor axis whenthe vibration source is excited by a first electrical signal that causesat least two vibration modes that are superimposed to create the firstelliptical path. In this particular aspect, at least one of thevibration modes is other than a pure longitudinal mode and other than apure bending mode. The elliptical motion has a major axis and minoraxis, one of which is aligned with the first direction an amountsufficient to cause motion of the driven element. Stated differently,the vibratory element moves the selected contacting portion in first andsecond elliptical paths each having a major and minor axis. At least oneof the major and minor axes does not coincide with the direction ofmotion resulting from the elliptical path with which the axis isassociated. This use of vibration modes other than pure bending or purelongitudinal can be used with other features described herein, includingthe resilient support, press-fit piezoelectric elements, and otherfeatures to name a few.

[0032] Another aspect of this invention is the use of elliptical motionthat does not align with the vibration element, but rather uses aninclined driving element and driven element. There is thus provided avibratory system for moving a driven element that includes a drivenelement movable in at least a first direction. The vibration source ismounted to a resonator to form a vibrating element; the vibratingelement having a selected contacting portion located to engage and movethe driven element. For this particular aspect, the selected contactingportion moves in a first elliptical path having a major axis and minoraxis at least one of which is not aligned with a longitudinal axis ofthe vibrating element. Advantageously, the longitudinal axis is inclinedat an angle α to a tangent to the driven element in the first directionat the selected contacting portion. The angle α is between about 10 and80 degrees when the selected contacting portion is drivingly engagingthe driven element. That angle is further refined as discussed later.This use of the inclined axis can also be used with other featuresdescribed herein, including the resilient support, press-fitpiezoelectric elements, and other features to name a few.

[0033] This invention also comprises methods for implementing the aboveapparatus and advantages. In particular, it includes a method ofconfiguring a vibratory system having a vibrating element with aselected contacting portion drivingly engaging a driven element to movethe driven element by moving the selected contacting portion in a firstelliptical motion. The method comprises analyzing that elliptical motionin a localized coordinate system in which at least one of the major andminor axes of the elliptical motion are not aligned with a predominantaxis of motion of the vibrating element. The method then varies thesystem design to incline at least one of the elliptical axes relative toa tangent to the driven element in the direction of motion at theselected contacting portion to more closely align at least one axis withthe tangent by an amount sufficient to achieve acceptable motion of thedriven element. The inclination is achieved by altering the ellipticalmotion or altering the relative orientation of the vibrating element andthe driven element, or both. That inclination is maintained duringoperation of the vibrating system.

[0034] There are advantages to orienting the localized coordinate systemrelative to the tangent. There are further advantages in setting theangle of inclination of the major axis of the first elliptical motion,designated by an angle β₁, to an angle that is greater than 5 degrees,and with the vibrating element and the driven element being inclinedrelative to each other by an angle α that is greater than about 5degrees.

[0035] The method also can include the provision of a vibrating elementhaving the selected contacting portion moving in a second ellipticalmotion to move the driven element in a second direction a desiredamount. A further variation of this method is to analyze that secondelliptical motion in a similar method to the first elliptical motion.Thus, the second elliptical motion is analyzed in a localized coordinatesystem in which at least one of the major and minor axes of the secondelliptical motion are not aligned with a predominant axis of motion ofthe vibrating element. The system design is altered to incline at leastone of the second elliptical axes relative to a tangent to the drivenelement in the second direction at the selected contacting portion tomore closely align the at least one axis of the second elliptical motionwith the tangent in the second direction by an amount sufficient toachieve acceptable motion of the driven element in the second direction.It is advantageous to maintain that inclination of the second ellipticalaxis during use of the system. The orientation of at least one of thefirst and second elliptical axes is typically a compromise that isselected to achieve less than optimum motion of the driven element inone direction in order to improve the motion of the driven element inthe other direction.

[0036] The method of analysis can also orient the localized coordinatesystem relative to the tangent, with the angle of inclination of themajor axis of the first elliptical motion being designated by an angleβ₁, and with the vibrating element and the driven element being inclinedrelative to each other by an angle α that is greater than about 5degrees. The angle of inclination of the major axis of the secondelliptical motion can be designated by an angle β₂, with at least one ofβ₁ and β₂ being greater than 5 degrees. Preferably, at least one of theangles β₁ and β₂ is between about 5-85 degrees. Moreover, in this methodthe vibratory element can be resiliently mounted to a base. The otherfeatures discussed herein could be used as well.

[0037] This invention allows the use of simplified driving systems. Onedriving system uses an inductive coil mounted on the piezoelectricelement and acting in cooperation with the inherent capacitance of thepiezoelectric element to form an L-C driving circuit. The wire coil canbe integrated into the vibratory element with the coil wire being alsoused as an electrical connection to the vibratory element, either inseries or parallel.

[0038] This invention also allows the use of a simple driver apparatusto control the operation of the vibrating element and its mechanicalresonator when the vibrating element has an inherent capacitance. Asmentioned, the piezoelectric element has an inherent capacitance. Thecontrol apparatus has at least one switching element allowing theapplication of a predetermined signal, such as the sinusoidal signaldiscussed herein. Further, there is at least one electrical resonatordriver circuit driving the vibrating element, where the driver circuitis electrically coupled to and activated by the switching element.Finally, there is at least one inductive coil electrically coupled tothe vibrating element to form an electric resonator together with thecapacitance of the vibrating element so the signal excites the drivercircuit at a predetermined frequency. The circuit resonances areselected to produce with the first and second signals at the first andsecond frequencies used to generate the first and second (and other)elliptical motions.

[0039] There are advantages if the coil is either mounted to thevibratory element or mounted to a common support with the vibratoryelement. Preferably the coil encircles a portion of the piezoelectricelement or the mechanical resonator. Further, it is useful to locate thedriver circuit and switching element more than four times further awayfrom the piezoelectric element than the coil. To make the constructioneven simpler, the same electrical conductor that is used to form thecoil can also connect the piezoelectric element to the drivercircuit—either in parallel or series.

[0040] Moreover, in a further embodiment there is provided apiezoelectric resonator driver circuit having a plurality ofunidirectional electrical gates to drive the piezoelectric element. Thedriver circuit is electrically coupled to and controlled by the controlelement; the piezoelectric element being electrically coupled to andpaired with one of the unidirectional gates. At least oneelectromagnetic storage element, such as an inductive coil, iselectrically coupled to the piezoelectric element so that theelectromagnetic storage element forms an electric resonator togetherwith the capacitance of the vibrating element. The unidirectionalelectrical gates can take the form of one or more diodes arranged toprevent a negative electrical voltage to the piezoelectric element. Thedriver circuit preferably resonates at a modulated predetermined firstresonant frequency selected to cause the vibrating element to cause theselected contacting portion to move in the first elliptical motion withsufficient amplitude to move the driven element in the first directionwhen the selected contacting portion engages the driven element. Thedriver circuit also preferably resonates at a modulated predeterminedsecond resonant frequency selected to cause the vibrating element tocause the selected contacting portion to move in a second ellipticalmotion with sufficient amplitude to move a driven element in the seconddirection when the selected contacting portion engages the drivenelement. Moreover, a resistor can be electrically coupled with theinductor and piezoelectric element and/or the gate element to maintainan input voltage to the piezoelectric element within predeterminedoperating parameters. Advantageously the diode(s) are coupled to theresistor in an orientation to prevent a negative voltage in thepiezoelectric element.

[0041] The control methods achieved by the control circuits broadlyinclude placing a control element in electrical communication with thepiezoelectric element and an inductor to alternate the electric signalbetween the inductor and piezoelectric element, with the piezoelectricelement providing a capacitance to function as a switched resonance L-Ccircuit so the electrical signal can resonantly drive the vibratingelement at a first frequency. Advantageously a portion of the inductoris formed on the resonator.

[0042] Further, the method for controlling the operation of thevibrating element includes placing the control element in electricalcommunication with the piezoelectric element and the inductor toalternate the electric signal between the inductor and piezoelectricelement, with the piezoelectric element providing a capacitance tofunction as a switched resonance L-C circuit so the electrical signalcan resonantly drive the vibrating element at a first frequency.Preferably, the method further includes selecting the first frequencyand configuring the vibrating element to cause a selected contactingportion of the vibrating element to move in a first elliptical path withsufficient amplitude to move a driven element in a first direction whenthe selected contacting portion engages the driven element.

[0043] Advantageously, the voltage to drive the piezoelectric element atthe first frequency is greater than the supply voltage to the circuit.Moreover, the method includes placing a resistor in electricalcommunication with the piezoelectric element to shape the electricalsignal provided to the piezoelectric element. Further, the methodpreferably forms, at least a portion of the inductor around a portion ofthe vibratory element. Finally, the inductor and piezoelectric elementpreferably provide a capacitance to function as a switched resonance L-Ccircuit so that a second electrical signal can resonantly drive thevibrating element at a second frequency, with the second frequency beingselected in conjunction with the configuration of the vibratory elementand its mounting to cause the selected contacting portion of thevibrating element to move in a second elliptical path with sufficientamplitude to move the driven element in a second direction when theselected contacting portion engages the driven element.

[0044] This invention also includes a method of configuring a vibratorysystem for moving a driven element that is supported to allow the drivenelement to move in a predetermined manner at a predetermined rate oftravel with a predetermined force. The system has a selected contactingportion of a vibratory element periodically engaging the driven elementto move the driven element, with one of the selected contacting portionand the driven element being resiliently urged against the other of theplaced in resilient contact with the selected contacting portion and thedriven element. The resilient contact is provided by a resilientsupport, with the vibratory element being caused to vibrate by avibration source that converts electrical energy directly into physicalmotion. The vibratory element includes the vibration source mounted in aresonator with the selected contacting portion being on the resonator.

[0045] The method of configuring this system comprises defining adesired elliptical motion of the selected contacting portion to producea desired movement of the driven element. At least one of the vibratoryelement and the resilient support is configured to cause the resonatorto vibrate in two modes of sufficient amplitude and phase that theselected contacting portion moves in an elliptical path when thevibratory source is excited by a first signal at a first frequencyprovided to the vibration source. The elliptical path is sufficientlyclose to the desired elliptical motion to achieve an acceptable motionof the driven element.

[0046] The method can further comprise defining a second desiredelliptical motion of the selected contacting portion to produce a seconddesired movement of the driven element. At least one of the vibratoryelement and the resilient support is configured to cause the resonatorto vibrate in two modes of sufficient amplitude and phase that theselected contacting portion moves in a second elliptical path when thevibratory source is excited by a second signal at a second frequencyprovided to the vibration source. The second elliptical path is selectedto be sufficiently close to the second desired elliptical motion toachieve an acceptable second movement of the driven element. Thevibration source is preferably selected to comprise a piezoelectricelement. Further, the resonator can be configured to cause the desiredmotion of the selected contacting portion, or the resonator incombination with a resilient support can be configured to cause thedesired motion.

[0047] In addition to the selected contacting portion moving the drivenelement in a first direction when the source of vibration is driven bythe first signal and moving the driven element in a second directionwhen the source of vibration is driven by the second signal, advantagesarise if the selected contacting portion further moves in the firstdirection when a single sinusoidal signal of a first frequency isapplied, and can also move in the first direction when the firstfrequency is dominant and superimposed with plural sinusoidal signals ofdifferent frequencies. In these latter instances, the second signal doesnot occur simultaneously with the first signal or else the first andsecond signals are of substantially different amplitude if they do occursimultaneously.

[0048] The method further includes placing the piezoelectric element incompression in the resonator during operation of the system bypress-fitting the piezoelectric element into an opening in theresonator. This is preferably achieved by stressing walls of theresonator past their yield point but not past their ultimate strengthpoint. The method further includes interposing a resilient elementbetween the base and the vibratory element to resiliently urge thevibratory element against the driven element during excitation at thefirst frequency. Further methods to implement the above features andadvantages are disclosed in more detail below.

[0049] A further method of this invention includes a method for movingobjects using vibratory motors having a vibration source placed in aresonator. The method comprises moving a selected contacting portion ofa resonator in a first elliptical motion in a first direction byconfiguring the resonator to simultaneously vibrate in two modes ofsufficient amplitude and phase to cause the first elliptical motion ofthe selected contacting portion when a single electrical signal isapplied to the vibration source. The method can further comprise placingthe selected contacting portion in resilient contact with a drivenelement to move the driven element. Additionally, the method can furthercomprise connecting a resilient element to the resonator to resilientlyurge the resonator against a driven element.

[0050] Other aspects of this method include selecting a piezoelectricelement for the vibration source and placing that piezoelectric elementin compression by press fitting it into an opening in the resonator. Theopening is preferably defined by at least two opposing walls that arestressed beyond their elastic limit when the piezoelectric element ispress-fit into the opening. There are advantages if the walls areselected to be curved.

[0051] When a piezoelectric element is used for the vibration source,the inherent capacitance of the piezoelectric lends itself to the use ofsimplified control systems while still maintaining system performance. Acontrol switch can activate a resonator driver circuit driving thevibrating element, with at least one electromagnetic storage element,such as an inductive coil, electrically coupled to the vibrating elementto drive the vibrating element when the driver circuit is activated. Thevibrating element increases charge when the electromagnetic storageelement discharges and the coil increases its charge when the vibratingelement discharges and the driver circuit is not activating thevibrating element. This construction basically places a control elementin electrical communication with the piezoelectric element and aninductor to alternate the electric signal between the inductor andpiezoelectric element, with the piezoelectric element providing acapacitance to function as a switched resonance L-C circuit so theelectrical signal can resonantly drive the vibrating element at a firstfrequency selected to achieve the desired elliptical motion at theselected contacting portion. This allows the voltage to drive thepiezoelectric element at the first frequency to be greater than thevoltage of the electrical signal provided to the control element. Thesame circuit can be used to provide the electrical signal for othervibration modes of the piezoelectric element.

[0052] Further, the coil can be mounted to the vibratory element ormounted to the same support as the vibratory element. Advantageously,the coil can encircle a portion of the vibratory element. Moreover, thecoil can be connected to the piezoelectric element in series, or inparallel. Additionally, the piezoelectric driver circuit can have aplurality of unidirectional electrical gates, such as a diode, can bepaired with the piezoelectric element to prevent or at least limit anynegative voltage to the piezoelectric element. In these driver circuits,the frequency is selected to achieve the desired motion of the selectedcontacting portion.

[0053] This invention further includes improved manufacturing andassembly aspects for vibratory apparatus used to move a driven element.In these aspects a vibration source is used that converts electricalenergy directly into physical motion. A resonator is provided having anopening defined by at least two opposing sidewalls that are stressedbeyond their elastic limit to hold the vibration element in compression.The vibration source is within that opening so that the vibrationelement is held in compression by the resonator under a defined preloadduring operation. Advantageously, the vibration source is press-fit intothe opening, and comprises a piezoelectric element. Further advantagesare achieved if the sidewalls are curved.

[0054] Moreover, it is useful to provide the piezoelectric element withat least two opposing edges that are inclined and located to engageedges of the opening to make it easier to press-fit the piezoelectricelement into the opening while reducing damage to the piezoelectricelement. The reduction of damage is especially desirable in view of thedamage that can occur to the piezoelectric element and to the resonatorif the inclined edges are absent. Preferably, there are at least twoopposing edges that have surfaces substantially parallel to the abuttingwalls defining the opening, and an inclined surface extending therefromto a contacting surface abutting one of the walls, with the contactingsurface exerting the preload.

[0055] In one embodiment, a resonator has a longitudinal axis with anopening partially defined by two sidewalls on opposing sides of thelongitudinal axis and two opposing end walls on the longitudinal axis. Apiezoelectric element is held in compression by the opposing end walls,with each of the sidewalls being stressed beyond its elastic limit tohold the piezoelectric element in compression. The resonator has aselected contacting portion, which moves in a first elliptical motionwhen the piezoelectric element is excited by the various electricalsignals described herein. There are advantages if the sidewalls arecurved, and if at least one of the end walls or two opposing sides ofthe piezoelectric element that engage the end walls have edges that areinclined to facilitate press-fitting the piezoelectric element into theopening and wherein the piezoelectric element is press-fit between theend walls. The sidewalls can be curved to bow away from thepiezoelectric element, or toward the piezoelectric element. Further, aportion of an elastic element for supporting the resonator can beinterposed between one of the end walls and the piezoelectric element.

[0056] The invention also includes a method of placing a piezoelectricelement in compression in a resonator, where the resonator has end wallsand sidewalls defining an opening sized to receive and place thepiezoelectric element in compression. The method includes increasing thedistance between opposing end walls enough to allow the piezoelectricelement to be forced between the end walls with a force that by itselfcould not force the piezoelectric element between the end walls in theoriginal state of the opening, and thereby placing the piezoelectricelement in compression while also stressing the sidewalls beyond theirelastic limit. The method can further include providing an inclinedsurface on at least one of either the end walls or the correspondingedges of the piezoelectric element, and forcing the piezoelectricelement into the opening by engaging said at least one inclined surface.

[0057] Moreover, the method can include pulling the opposing end wallsapart while forcing the piezoelectric element into the opening. In onefurther embodiment, the method includes curving the sidewalls away fromeach other, and urging the opposing, curved sidewalls toward each otherin order to move the end walls away from each other and then placing thepiezoelectric element between the end walls. In another embodiment, themethod includes curving the sidewalls toward each other, and urging theopposing, curved sidewalls away from each other in order to move the endwalls away from each other and then forcing the piezoelectric elementbetween the end walls. The various methods can also include interposinga resilient mount for the piezoelectric element between thepiezoelectric element and one of the end walls.

[0058] There is also advantageously provided a piezoelectric elementconfigured to be press-fit into an opening in a resonator. The openingis defined by sidewalls located on opposing sides of a longitudinal axisthrough the opening and separated by a first dimension, with opposingend walls located on the longitudinal axis and separated by a seconddimension. The piezoelectric element has a first dimension that issmaller than the first dimension of the opening and has a seconddimension larger than the second dimension of the opening and selectedto stress the sidewalls beyond their elastic limit when thepiezoelectric element is inserted into the opening. The piezoelectricelement has inclined edges corresponding in location to edges of the endwalls when the piezoelectric element is aligned to be inserted into theopening. The above variations can also be used with this embodiment,including curved sidewalls, a resilient support for the resonatorinterposed between one end wall and the piezoelectric element duringuse, and at least one inclined edge corresponding in location to an edgeof the end wall when the piezoelectric element is aligned to be insertedinto the opening.

[0059] There is also advantageously provided a resonator 24 for use witha piezoelectric actuator. The resonator has a continuous walled,externally accessible opening sized to receive a piezoelectric elementor other source of vibration, and to hold that element in compression.The opening is optionally, but preferably defined in part by opposingsidewalls that are curved. The walls can be curved toward, or away fromthe opening and the piezoelectric element therein. Preferably thesidewalls are curved, and have a uniform cross section for a substantialportion of the length of the sidewall. A substantial length includesover half the length, preferably more, and ideally the entire lengthuntil the junction with the end walls is reached. Rectangular crosssections are preferred.

[0060] Given the present disclosure, further methods will be apparent toone skilled in the art to implement the above features and advantages,and the features and advantages discussed below. Further, other objectsand features of the invention will become apparent from consideration ofthe following description taken in connection with the accompanyingdrawings, in which like numbers refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

[0061]FIGS. 1a-1 d show a plan side view, side perspective view, endview, and bottom view, respectively, of a first embodiment of thisinvention;

[0062]FIG. 2 shows a top view of the vibratory element of FIG. 1;

[0063]FIG. 3 shows an end view of FIG. 2;

[0064]FIG. 4 shows a perspective view of a second embodiment of thisinvention;

[0065]FIG. 5 shows a side view of a third embodiment of this inventionusing a C-clamp configuration;

[0066]FIG. 6 shows a perspective view of a fourth embodiment of thisinvention driving multiple elements;

[0067]FIG. 7a shows a perspective view of a vibratory element of thisinvention containing a press-fit piezoelectric element;

[0068]FIG. 7b shows an enlarged portion of the vibratory element of FIG.7a during assembly;

[0069]FIG. 8 shows a fifth embodiment of this invention having apress-fit piezoelectric element;

[0070] FIGS. 9 shows a top view of a press-fit embodiment beforedeformation;

[0071]FIG. 10 shows a top view of the embodiment of FIG. 9 afterdeformation by a cylindrical wedge;

[0072]FIG. 11 shows a sectional view along line 11-11 of FIG. 10;

[0073]FIG. 12 shows a top view of an alternative embodiment of FIG. 9using a rectangular wedge;

[0074]FIG. 13 shows an embodiment with the piezoelectric element offsetfrom the axis of a resonator;

[0075]FIG. 14 shows an embodiment with an insert offsetting the forcefrom the piezoelectric element from the centerline of a resonator;

[0076]FIG. 15 shows an embodiment with the piezoelectric element skewedrelative to the axis of the resonator;

[0077]FIG. 16 shows an embodiment with the piezoelectric elementpositioned between selectably positioned inert elements and compressedby a threaded fastener;

[0078] FIGS. 17-19 show suspension configurations for a vibratoryelement of this invention having a pivoted support for the vibratoryelement;

[0079] FIGS. 20-21 show suspension configurations for a vibratoryelement of this invention having a resilient support;

[0080]FIG. 22 shows a suspension configuration for a vibratory elementof this invention having a pivoted support;

[0081] FIGS. 23-24 show configurations of a vibratory element and drivenelement of this invention with the longitudinal axes of the parts inparallel but offset planes;

[0082]FIG. 25 shows a configuration of a vibratory element and drivenelement of this invention with the axes of the parts inclined at anangle;

[0083]FIG. 26 is an end view of the configuration of FIG. 25;

[0084] FIGS. 27-29 show configurations of two vibratory elements locatedin parallel but offset planes relative to the plane of the drivenelement;

[0085]FIG. 30 shows a configuration of two vibratory elements located inthe same plane but offset from the plane containing the driven element;

[0086]FIG. 31 shows a configuration of two vibratory elements and onedriven element with the driven elements located above and below thedriven element and at inclined angles relative to the driven element andfacing each other;

[0087]FIG. 32 shows a configuration of two vibratory elements and onedriven element with the driven elements located above and below thedriven element and at inclined angles relative to the driven element andfacing the same direction;

[0088]FIG. 33 shows a configuration of two vibratory elements and onedriven element with the driven elements located on one common side ofdriven element and at inclined angles relative to the driven element andfacing the same direction;

[0089]FIG. 34 shows a configuration of two vibratory elements and onedriven element with the driven elements located on one common side ofthe driven element and at inclined angles relative to the driven elementand facing each other;

[0090]FIG. 35 shows a configuration of two vibratory elements and onedriven element with the driven elements located on opposing sides of thedriven element and at inclined angles relative to the driven element andfacing the same direction;

[0091]FIG. 36 is an end view of the configuration of FIG. 35;

[0092] FIGS. 37-40 show configurations of three vibratory elements andone driven element,

[0093]FIG. 41 shows a front view of a configuration of six vibratoryelements and one driven element;

[0094]FIG. 42 shows a left side view of the configuration of FIG. 41;

[0095]FIG. 43 shows a diagram of the elliptical motion of the selectedcontact portion of this invention;

[0096] FIGS. 44-51 show graphical presentations of various aspectsaffecting the elliptical motion of the contacting portion depicted inFIG. 43;

[0097]FIG. 52 shows a perspective view of a vibratory element having aslot in the resonator in the same face of the resonator in which theopening is formed to receive the piezoelectric element;

[0098]FIG. 53 shows a perspective view of a vibratory element having aslot in the resonator and an opening with curved ends to receive thepiezoelectric element;

[0099]FIG. 54 shows a perspective view of a vibratory element having awider slot in the resonator;

[0100]FIG. 55 shows a perspective view of a vibratory element having aslot in the resonator in a face of the resonator that is different fromthe opening formed to receive the piezoelectric element;

[0101]FIG. 56 shows a perspective view of a vibratory element having an“H” shaped opening to receive the piezoelectric element;

[0102]FIG. 57 shows a perspective view of a vibratory element having aslot defining two beams in the resonator with the piezoelectric elementbeing located in one beam;

[0103]FIG. 58 shows a perspective view of a vibratory element having ahole in the resonator to alter the performance of the vibratory element;

[0104]FIG. 59 shows a perspective view of a vibratory element having anenlarged mass at a proximal end of the resonator;

[0105]FIG. 60 shows a perspective view of a vibratory element havingfour sidewalls defining the opening in which the piezoelectric elementis placed;

[0106]FIG. 61 is a cross sectional view of a vibratory element enclosingthe piezoelectric element in a cavity within the resonator;

[0107]FIG. 62 is a side view of a vibratory element having severalselected contacting portions to engage a driven element;

[0108] FIGS. 63-66 are electrical schematics for systems to provideelectronic signals to the vibratory elements of this invention;

[0109]FIG. 67 is a plan side view of a piezoelectric element havingspecially configured ends;

[0110]FIG. 68 is a perspective view of the piezoelectric element of FIG.67;

[0111]FIG. 69 is a side sectional view of a die used to form thepiezoelectric elements of FIGS. 67-68;

[0112]FIG. 70 is a schematic view of a vibrating driving element and avibrating driven element of a further embodiment of this invention;

[0113] FIGS. 71-72 are schematic views of several positioning sensingconfigurations;

[0114]FIG. 73 shows cross-sections for resonator elements of thisinvention;

[0115]FIG. 74 shows a schematic view of a vibrating element with acurved spring suspension system;

[0116]FIG. 75 shows a sequence for press-fitting a piezoelectric into anopening in a resonator;

[0117]FIG. 76 shows a pull-fit process for a piezoelectric motorassembly of this invention;

[0118]FIG. 77 shows a further embodiment of a piezoelectric motorassembly of this invention;

[0119] FIGS. 78-80 show further embodiments in which a coil isintegrated with or associated with the motor or motor components of thisinvention; and

[0120]FIG. 81 shows the motion of a selected contacting portion of thisinvention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0121] Several embodiments of the motor of this invention will bedescribed, following which a number of theoretical and practicaloperational and design aspects of the motors are described. Referring toFIGS. 1-3, and as described in detail at various locations, thepiezoelectric motor assembly 20 has an element that converts electricalenergy into macroscopic mechanical motion. This is achieved by using asingle electrical signal to generate at least two vibration motions at apredetermined location of a vibration element. The at least twovibration motions result in an elliptical motion at the predeterminedlocation. The elliptical motion is selected to cause the vibratingelement to engage a driven element during a time corresponding to atleast a portion of travel in direction of a long axis of the ellipse,and to disengage or slide over the driven element during a timecorresponding to travel in the opposite direction. A second, singlefrequency results in a second elliptical motion in an opposing directionto move the driven element in an opposing direction. The desired motionis used to determine the elliptical motion needed, and the variouscomponents of the system are designed to achieve that motion. The use ofa single frequency to generate elliptical motion and the simplicity ofthe resulting design allow a low cost, high reliability motor.

[0122] The motor assembly 20 has a vibration source 22 that convertselectrical energy directly into physical motion. The vibration source 22is preferably a piezoelectric element and comprises a block ofpiezoelectric material, or a multi-layer piezoelectric so that themotion of the various elements combine to increase the movement indesired directions. The shape of the piezoelectric 22 can vary, but itadvantageously has a longitudinal axis 25 along its direction ofgreatest motion. The piezoelectric 22 is mounted to, and preferablyinside, a resonator 24. The piezoelectric 22 and resonator 24 comprise avibration element 26 or motor 26.

[0123] The piezoelectric material is preferred because it reacts quicklyto applied voltages. While the resulting deflection for a given voltageis small, about 0.1% or less of the length of the piezoelectric, andsmaller in other directions, the resulting force is large so thatvibration resonance can be achieved.

[0124] The source 22 can also comprise electrostrictive materials,magneto-restrictve materials (e.g., Terfenol), or other materials thatcan be used to excite vibrations, according to other embodiments.Preferably, the vibration source 22 comprises materials or devices thatconvert electrical energy directly into physical motion. For ease ofreference, the vibration source 22 will be referred to and describedherein as piezoelectric 22.

[0125] To avoid confusion between motor 26 and motor assembly 20, theterminology “vibration element” 26 will be used in most cases to referto the combination of the piezoelectric element 22 and the resonator 24.

[0126] The resonator 24 can have various shapes, but is illustrated ashaving a rectangular shape with a rectangular cross-section. In order tomount the piezoelectric 22 inside the resonator 24, it is useful to forma cavity or an opening 28 in the resonator 24 to hold the piezoelectricelement 22. The opening 28 is shown as extending entirely through aportion of the resonator 24 to form a rectangular opening, withsidewalls 29 which define the sides of opening 28, the sidewalls beinglocated on opposing sides of the longitudinal axis extending through theopening 28, and with end walls 31 being located on the longitudinal axisextending through the opening 28. The opening 28 is thus advantageouslydefined by continuous walls that enclose the opening. Appropriateelectrical connections are provided to the piezoelectric 22 and maycomprise electrical connections of various types, but which areillustrated as wires 30.

[0127] Application of large voltages to an unrestrained piezoelectric 22can damage the piezoelectric. Thus, the piezoelectric 22 isadvantageously placed in compression along at least its longitudinalaxis, by end walls 31. This also causes a preload, which optimizes thepiezoelectric lifetime and performance. But a compressive force is notnecessarily used if other vibration sources are used that do not requirecompression, or that do not benefit from compression. Several ways topreload the piezoelectric element 22 are discussed later.

[0128] In order to make it easier to place the piezoelectric element 22in compression, the opening 28 is advantageously enclosed on opposingsides, and preferably enclosed on opposing ends of the longitudinal axisof piezoelectric 22. This arrangement provides opposing surfaces thatcan be used to provide compression to the piezoelectric 22. One way topreload the piezoelectric 22 is by movably extending a screw 32 througha threaded opening in the proximal end 35 of resonator 24 so that adistal end of the screw can be moved to compress the piezoelectric 22against one end of the opening 28 in the resonator 24. Since thepiezoelectric material is brittle, a protective cap 34 is interposedbetween the distal end of the screw 32 and the adjacent end of thepiezoelectric 22. The cap 34 is made of a protective material thatallows the rotation of the screw 32 to compress the piezoelectric whilenot breaking or cracking the piezoelectric 22. Metal caps 34 arepreferred, but some lubricant or rotational accommodating design isadvantageously provided in order to avoid at least some damage to thepiezoelectric 22 from rotation of the screw 32. Other clamping methodsof the piezoelectric 22 without a screw and/or a protecting plate can beused, such as expansion or shrinkage of the opening 28. Additional waysare described below, and other ways will become known to those skilledin the art given the present disclosure.

[0129] When a voltage is applied to the piezoelectric element 22, thepiezoelectric element extends along longitudinal axis 25, and thatcauses the vibration element 26 to also extend in length, in part byelongating the smaller cross-section sidewalls 29. The vibration of thepiezoelectric 22 excites a longitudinal mode in the vibration element 26which causes the distal end 36 opposite the screw 32 to move back andforth along the longitudinal axis 25. In addition to that longitudinalmotion, bending modes of the vibration element 26 will be excited whichare transverse to the longitudinal axis 25. For the illustratedembodiment, a first preferred bending mode occurs in the directionindicated by arrow 38, which is perpendicular to the longitudinal axis25 in the plane of the paper on which the illustration is placed inFIG. 1. A second, preferred lateral bending mode occurs along an axisorthogonal to the paper on which the illustration is placed in FIG. 1,and is denoted by axis 40. In practice, the vibration modes are oftencombinations of various modes involving motion along and rotation aboutmultiple axes.

[0130] Advantageously, the components of the invention are configured sothat the various modes are excited at or very close to their respectiveresonance frequencies in order to increase the amplitude of motion alongthe longitudinal axis 25 and preferably only one of the lateral axes 38,40. As discussed later, the lateral bending can be excited either byasymmetrical placement of the piezoelectric 22 relative to the resonator24, or by an asymmetrically placed mass on the vibration element 26, orby a mounting of the piezoelectric element 22, or by shaping theresonator 24 to resonate with a desired lateral motion, or by othermechanisms, some of which are discussed later.

[0131] In the embodiment depicted in FIGS. 1-2, the motion along lateralaxis 38 is preferably substantially greater than the motion alonglateral axis 40. Substantially greater refers to a difference by afactor of at least 3, and preferably a factor of 10.

[0132] A driven element 42 is placed in contact with a selected contactportion 44 of the vibration element 26. As illustrated in FIGS. 1-2, theselected contact portion 44 comprises an edge of the vibrating element,although other locations could be used. As used herein, unless otherwiseindicated, the term “edge” should be construed to include a corner wheremultiple surfaces converge, as for example, in the corner of arectangular cross-sectional rod where three planar surfaces converge(and where three edges converge). Moreover, other shapes of contactingsurfaces could be used other than an edge. For example, a beveledsurface inclined at an angle selected to place contacting surface 44into flat engagement with the engaging surface of driven element 42could be used. Given the present disclosure, many configurations can bederived to ensure that the engaging surface 44 provides the neededengagement to move the driven element 42.

[0133] As illustrated, the driven element 42 comprises a rod with acylindrical cross-section, although other shapes of driven elements canbe used. The centerline 25 of the vibration element 26 and a centerline45 of rod 42 are in the same plane, and separated by an angle α of about30 degrees as measured in that plane. The orientations of thecenterlines 25, 45 and the angle α will vary with the particularapplication. The angle α is difficult to analytically determine, and ispreferably adjusted according to the motor design. Typically it isbetween 10 and 80 degrees, and preferably between 20 and 60 degrees. Thedriven element 42 is supported so it can move along the longitudinalaxis 45 of the driven element 42. The driven member is supported so thatit can move relative to the vibration element 26, which is effectivelyheld stationary in the illustrated embodiment. The driven element 42translates along the axis 45, as explained in greater detail below.

[0134] As illustrated, the support of the driven element 42 can beachieved by wheels 46, which provide a low resistance to motion alongthe axis 45. This support is achieved here by placing an inclinedsurface on the wheels 46, which abut the curved sides of rod-like drivenelement 42 and rotate as the rod translates along axis 45. The wheelsare located on the side of the driven element 42 opposite the selectedcontact portion 44, with the contact portion 44 also being furtherlocated between two wheels 46 in a direction along the axis 45, so thatthe wheels 46 and selected contact portion 44 restrain motion of thedriven element 42 in all directions except along axis 45. The wheel 46could also contact the driven element 42 using a flat edge of the wheelconcentric with the rotational axis 65, as illustrated in FIG. 74. Thewheels 46 could also have contoured peripheries configured to engagemating shapes on adjacent portions of the driven element 42 in order toappropriately support and guide the driven element 42. Given the presentdisclosure, a variety of movable support configurations will be apparentto those skilled in the art.

[0135] The vibration element 26 is advantageously resiliently urgedagainst the driven element 42, and FIGS. 1-2 show one of many ways toachieve this. The elliptical motion 100 of the selected contactingportion 44 is preferably an unrestrained motion, one that occurs whetheror not the contacting portion 44 engages a driven element, and one thatis achieved without relying on any resistance from being urged againstthe driven element 42. Nevertheless, the selected contacting portion 44is advantageously resiliently urged against the driven element 42 inorder to enhance the driving engagement of the driving and driven parts.

[0136] A spring 50 made of flat, elongated spring material is bent intoan “L” shape with opposing ends 50 a, 50 b. A first end 50 a of thespring is fastened to a base 52. A second end 50 b of the spring isfastened to the end of the vibration element 26 through which the screw32 extends, with a hole in the end 50 b of spring 50 allowing passage ofthe screw. A first leg of the spring 50 which contains end 50 a isgenerally parallel to the longitudinal axis of vibration element 26, andthe second leg of the spring 50 that contains the end 50 b is generallyparallel to the axis 38, with the two legs being generally perpendicularto each other. The spring 50 resiliently urges the vibration element 26against the driven element 42 at the selected contact portion 44.Variations in the location of the mounting at end 50 a, 50 b can be usedto vary the pre-load with which the vibration element 26 is urgedagainst the driven element 42. As discussed later, variations in theshape, cross-section, location, and form of the resilient element 50 arepossible and can be used to achieve a desired vibration mode.

[0137] The spring 50 is designed to optimize the vibrationcharacteristics of vibration element 26 as well as provide a sufficientrange of flexibility to insure contact between the driven element 42 andvibration element 26. This contact and a defined range of contactpressure should be maintained throughout the life of the motor assembly20. The spring 50 advantageously compensates for manufacturingtolerances and uncertainties and also can compensate for wear that mightreduce the size of the vibration element 26 at the selected contactportion 44.

[0138] As discussed further below, during operation the vibrationelement 26 might touch the driven element 42 only part of the time dueto the vibration and in such a case the spring 50 preferably is designedto ensure suitable engagement. The spring constant and the location ofthe spring can be used to adjust the percentage of contact andnon-contact time. This allows a designer the ability to configure themotor assembly 20 to ensure the resulting engagement between engagingportion 44 and driven element 42 is with sufficient force to move thedriven element 42 with sufficient force to achieve the desiredobjectives of motor assembly 20. Moreover, variations in the dimensionsaffecting the engagement of the selected engaging portion 44 and thedriven element 42 will be accommodated by the mounting system, such asspring 50, that resiliently urges the contacting parts into engagement.This flexibility in manufacturing tolerances allows a reduction inmanufacturing costs and in alignment tolerances and costs.

[0139] In the depicted embodiment the wheels 46 are both rotatablymounted to axles connected to the base 52. Other schemes of mounting thedriven element 42 are possible given the present disclosure. Forexample, the base 52 could support one or more projections havingaligned holes into which linear bearings are preferably placed, with theelongated driven member 42 extending through the holes. Thisconfiguration would allow an elongated driven member 42 to translatealong an axis, but would restrain other motions. The motor can be assmall as 25×25×5 mm³ or even smaller.

[0140] Operation:

[0141] Referring primarily to FIGS. 1-2, when an electrical signal ofsuitable frequency, waveform and voltage is applied to the piezoelectricelement 22 the vibration element 26 starts to move the rod 42. For theembodiment shown, preferred waveforms are sine waves or rectangularlyshaped waves. The direction of the linear motion generated is determinedby the frequency. A motor assembly 20 operating, for example, at about35 kHz in one direction and at about 60 kHz in the other direction isbelieved to be suitable for a variety of potential uses. Other frequencypairings are possible and will vary with a variety of factors concerningthe design of motor assembly 20. The operating frequencies can bechanged by changing the design of the various components, with theoperating frequencies being selected to be inaudible by humans and bymost pets in some preferred embodiments. The operating voltage will varywith the type of piezoelectric 22 or other vibration source used. Amulti-layered piezoelectric 22 operating at 6 volts peak-to-peakamplitude is believed useful for a variety of applications.

[0142] The vibration of the piezoelectric element 22 makes the vibrationelement 26 vibrate in a way so that the selected contact portion 44performs an elliptic motion relative to the driven element 42. Asdiscussed below, the vibration of the piezoelectric 22 excited at afirst frequency makes the vibration element 26 vibrate in a way so thatthe selected contact portion 44 performs a first elliptic motion 100 arelative to the driven element 42. The elliptical motion is achieved byhaving the first signal excite two resonant modes of the resonator 24,resulting in the desired elliptical motion 100 a—preferably withoutrequiring engagement with the driven element 42 to achieve thiselliptical motion. That first elliptical motion 100 a moves the drivenelement 42 to the right as depicted in FIG. 1.

[0143] Moreover, vibration of the piezoelectric 22 excited at a secondfrequency makes the vibration element 26 vibrate in a way so that theselected contact portion 44 performs a second elliptic motion 100 brelative to the driven element 42 in a different direction andorientation than that of elliptical motion 100 a, and preferably, butoptionally, in a direction opposite that of elliptical motion 100 a. Asdepicted, the second elliptical motion is clockwise and that will movethe driven element 42 in an opposite direction, to the left as depictedin FIG. 1. Typically, the elliptical motions 100 a, 100 b do notoverlap, but have different major and minor axes, amplitudes andorientations. Ideally, the elliptical motions 100 a, 100 b overlap. Theelliptical motions 100 a, 100 b are preferably achieved withoutrequiring that the selected contact portion 44 engage the driven element42.

[0144] This results in the selected contacting portion 44 moving thedriven element 42 in a first direction when the source of vibration isdriven by the first signal, and moving the driven element in a seconddirection when the source of vibration is driven by the second signal.But advantageously the selected contacting portion further moves in thefirst direction when a single sinusoidal signal of a first frequency isapplied. Moreover, the selected contacting portion 44 can also move inthe first direction when the first frequency is dominant andsuperimposed with plural sinusoidal signals of different frequencies. Inthis later instance, the second signal either does not occursimultaneously with the first signal or it is of substantially differentamplitude if it occurs simultaneously with the first signal. Bydifferent in signal amplitudes a factor of about 10 is consideredsubstantially different, and preferably the amplitudes differ by afactor of 100 or more. The result is that the elliptical motion 100 canbe achieved by a simple sinusoidal signal. Alternatively, it can beachieved by complex signals of different frequencies—for example, thecomplex frequencies that are superimposed to generate sawtooth waves.

[0145] During driving engagement of the selected contacting portion 44with the driven element 42, it is believed that the elliptical motion100 consists of a phase where the vibration element 26 is pressedagainst the driven element 42 and a phase where this is not the case.The motion component of the vibration element that has the directionalong the longitudinal axis 45 of the driven element is partlytransferred to the driven element by the friction between the vibrationelement 26 and the driven element 42. In the second phase the vibrationelement 26 moves in the opposite direction. In this second phase thevibration element does not transfer any motion component parallel to theaxis 45 because the vibration element 26 is not pressed against thedriven element.

[0146] In contrast to other vibrating motor designs, the requiredmanufacturing tolerances are believed to be significantly looser so thatno precise manufacturing is needed to alternate between the contact andno contact situations. The necessary equilibrium is created by thedesign, specifically including spring and the mass of the vibrationelement 26.

[0147] Because the high frequencies (over 30 kHz) and small motions makeit difficult to actually determine the contact, it is also believedpossible that there is always contact between the vibration element 26and the driven element 42. In that situation, the motion of the drivenelement 42 is believed to be caused by the difference in force at theselected contact portion 44 caused by the elliptical motion of thecontact portion 44 which provides a resultant force in only onedirection, or primarily in only one direction, thus driving the drivenelement 42 in that direction. Further discussions of this ellipticalmotion and a number of design aspects are discussed below.

[0148] Whatever the actual mechanism, the driven element performs alinear motion with the direction of the motion being determined by themotion of the selected contact portion 44 of the vibration element 26.If the contact portion does a counterclockwise elliptical motion, thedriven element 42 will move to the right as depicted in FIG. 1. If themotion is clockwise, it will move in opposite direction.

[0149] It is possible that the vibration element 26 will also be excitedto move along axis 40, which could result in rotation of the cylindricalrod-like driven element 42. Depending on the relative magnitudes of themotion of the selected contact portion 44 and depending on itsorientation and contact with the driven element 42, and if the bearingsupports are properly configured, both translation and rotation couldsimultaneously occur.

[0150] Further, referring to FIG. 2, it is believed possible to selectthe axis with the largest motion to be longitudinal axis 25, but toselect the lateral axis 40 as having the next largest and only othersignificant motion. In that instance the motor assembly 20 would cause arotation of the rod-like driven element 42 about longitudinal axis 45.To provide this rotational motion, the selected contact portion 44 wouldhave to provide an elliptic motion having a substantial portion of itsmotion in a plane generally orthogonal to the axis 45 of the drivenelement 42 in order to impart rotational motion to the driven element.The direction of rotation would again depend on the direction in whichthe selected contact portion 44 performs the shape of the ellipse.

[0151] Moreover, it is believed possible to select the axes with thelargest two motions, and only significant motions, to be the lateralaxes 38, 40, which could again result in an elliptical motion of theselected contact portion 44 in a manner that engages the driven element42 to rotate it about longitudinal axis 45 during one portion ofmovement and to disengage sufficiently to prevent motion or noticeabledetrimental motion in the other portion of movement of the selectedcontact portion 44.

[0152] An alternative embodiment is shown in FIG. 4, where instead of anelongated driven element 42 a rotatable wheel 60 is mounted to be drivenby the vibratory element 26 having a portion placed in contact with anappropriately located driven surface 62 on the wheel 60. In thisembodiment the wheel 60 is mounted to rotate about rotational axis 65 ona bearing. The driven surface 62 is preferably placed on a side 64 ofthe wheel located in a plane orthogonal to the rotational axis 65 aswith driven surface 62 a, or placed along a surface concentric 62 b withthe axis 65. The wheel 60 could comprise a variety of elements,including a gear. The selected contact portion 44 of the vibratoryelement 26 engages the driven surface 62 to cause movement of the wheel60 about the rotational axis. The wheel 60 will rotate in the oppositedirection of the motion of the contact point around the elliptical pathtraveled by the contact portion 44. Thus, if the contacting portion 44of the vibration element 26 moves clockwise the wheel 60 will movecounterclockwise, so that the contact portion on the wheel and on thevibration element share the same motion while they are in contact.

[0153]FIG. 5 shows a further embodiment. The motor assembly 20 has avibration element 26 that contains a resonator 24 in the shape of aC-clamp 74. The piezoelectric element 22 is held in the clamp. Totransmit the motions, a first electrical signal causes the piezoelectricelement 22 to move in the vibration element 26 which causes thecontacting portion 44 to move in a first an elliptical motion 100 a.

[0154] The piezoelectric element 22 is clamped by the screw 32 whichextends through leg 73 and presses against insert plate 34 to compressthe piezoelectric element 22 between the plate 34 and an opposing leg 75of the C-clamp resonator 74. This clamping causes pre-load in thepiezoelectric element 22, which increases and preferably optimizes thelifetime and performance of the piezoelectric element 22.

[0155] The legs 73, 75 of the C-clamp between which the piezoelectricelement 22 is held, could be of similar stiffness, but areadvantageously of different stiffness. Advantageously one leg 73 is atleast a factor of 10 times stiffer than the opposing leg 73. The moreflexible leg 75 vibrates with larger amplitude than the stiffer leg 73.The selected contacting portion 44 is preferably located on the lessstiff leg 73 in order to achieve a larger amplitude of motion at theselected contacting portion 44. Moreover, in this configuration the leg73 is placed in bending stress, with the largest stress being adjacentthe interior end of the leg. A notch 77 can be placed adjacent to thatlocation in order to localize the bending so that the leg 75 pivotsabout the notch 77.

[0156] A spring element 50 has a first end 50 a connected to the base 52and a second end 52 b connected to a vibration element 26 to keep thevibration element in contact with the driven element 42. The second end50 b is shown as connected to the head of the screw 32 although otherconnections to the resonator 74 could be used. In this embodiment thespring 50 is depicted as a tension coil spring. The resonator 74 isloosely pinned by pin 78 extending through hole 80 and into the base 52so the resonator 74 can pivot about pin 78. The pin 78 is offset fromthe line of action of spring 50 so that the contacting portion 44 isresiliently urged against driven element 42.

[0157] The spring 50 is under tension in the depicted configuration. Thespring 50 provides a sufficient range of flexibility to ensure contactbetween the driven element 42 and the vibration element 74. This contactand a defined range of contact pressures are advantageously maintainedthroughout the life of the motor assembly 20. The spring 50advantageously is designed to compensate for manufacturing uncertaintiesand wear that might reduce the size of the vibration element 26 at theselected contact portion 44.

[0158] To prevent the driven element 42 from separating from thevibration element 26, wheels 46 connected to the base 52 are provided aspreviously discussed. Alternatively, the base 52 can be equipped withsidewalls 80 having holes through which the driven element 42 extends inorder to support the driven element while allowing it to move along itsdesired translational axis. Advantageously, the holes in the sidewalls80 are designed to reduce friction, and thus could have linear bearingssupporting the driven element 42. If the holes in the sidewalls 80 areenlarged so that they do not permanently contact the driven element 42,they function as auxiliary bearings instead and protect the drivenelement 42 from being forcefully pushed into the vibration element 26 byexternal forces, which could be damaging to the vibration element 26 aswell as its suspension.

[0159] When an electrical signal of suitable frequency, waveform andvoltage is applied to the piezoelectric element 22 the vibration element46 starts to move the driven element 42. The direction of the linearmotion generated is determined by the frequency. Changing theconfiguration of various components of the motor assembly 20, asdiscussed further below, can change the operating frequencies. In thedepicted example, a multi-layered piezoelectric element is used thatcould operate the motor assembly 20 on 6V peak-to-peak amplitude todrive a cylindrical rod 44.

[0160] The vibration of the piezoelectric 22 at a first frequency makesthe vibration element 26 vibrate in a way so that the selected contactportion 44 performs a first elliptic motion relative to the drivenelement 42. The elliptical motion consists of a phase where thevibration element 26 is pressed against the driven element 42 and aphase where this is not the case, as discussed in further detail below.If the selected contact portion 44 moves in a counterclockwiseelliptical path 100 a as depicted, the driven element 42 will move tothe right as depicted in FIG. 5.

[0161] Advantageously, the vibration of the piezoelectric 22 excited ata second frequency makes the vibration element 26 vibrate in a way sothat the selected contact portion 44 performs a second elliptic motion100 b relative to the driven element 42 in a direction opposite that ofelliptical motion 100 a. As depicted, the second elliptical motion isclockwise and that will move the driven element 42 in an oppositedirection, to the left as depicted in FIG. 5. Typically, the ellipticalmotion 100 a, 100 b do not overlap, but have different major and minoraxes, amplitudes and orientations. Ideally, the elliptical motions 100a, 100 b overlap. The vibrating element 26 could be configured to causethe second elliptical motion 100 b to be in a different orientation, asfor example, to rotate a driven element 42.

[0162] In more detail, vibration of the piezoelectric element 22 causesthe vibration element 26 to begin oscillating about the pin 78, whichcauses the contact portion 44 to have an up-and-down motion and aback-and forth motion along its elliptical path 100. The up-down motionand the back-forth motion are out of phase, and the contact portion 44thus has an elliptical motion along one of paths 100 a, 100 b. Thatcauses the rod-like driven element 42 to begin motion. The rotation ofthe vibration element 26 can be caused by interaction of the contactingportion 44 with the driven element 42, which may be viewed as conservingangular momentum about the pin.

[0163] The vibratory motor 26 of FIG. 5 could be used with a rotatingdriven element 42 as depicted in FIG. 4, and could be used in otherdriving arrangements.

[0164]FIG. 6 shows a further embodiment in which the vibrating element26 is mounted in a stationary manner, and the driven element 42 isresiliently urged against the vibrating element. If the driven element42 is elongated, and especially if it comprises a rod or other structurethat is flexible, merely pressing the driven element against thevibrating motor 26 may cause the parts to resiliently urged intocontact. That requires the support of the driven element 42 to be suchthat a resilient support is inherently provided by the flexibility ofthe driven element. If that is not the case, a resilient support must beprovided for the driven element 42, or a resilient support can beprovided in addition to the flexibility of the driven element. Such aresilient support is illustrated schematically by springs 50 a, 50 b,resiliently urged against the selected contacting portion 44 a, 44 b ofthe vibrating element 26.

[0165] In this embodiment, the vibration element 26 is configured with aspecial shape so that there are more than one, and preferably a numberof selected contacting portions 44 a, 44 b, . . . 44 n. The ability touse different portions of the vibrating element 26 to generate a desiredelliptical motion 100 resulting from free vibration modes excited at aspecified frequency, offers the ability to have a variety ofarrangements. For each of several separate excitation frequencies, adifferent selected contacting portion 44 can resonate in a predeterminedelliptical motion 100. Alternatively, the same selected contactingportion 44 may resonate at a different excitation frequency to cause anelliptical motion but in a different orientation. Preferably theelliptical motion is in opposite direction to reverse the motion of thedriven element, but other motions are possible depending on the needs ofthe user. As a result, several driven elements 42 a through 42 n thatare resiliently urged against separate and corresponding selectedcontacting portions 44 a through 42 n, can be individually controlled.

[0166] For example, it is believed possible to have one driven element42 a translate, and another driven element 42 b rotate, by generatingappropriately orientated elliptical paths 100 a, 100 b respectively, atselected contacting portions 44 a, 44 b, respectively. The generation ofthe elliptical paths 100 a, 100 b is preferably caused by a singleexcitation frequency to piezoelectric element 22, which causes asufficiently resonant vibration to generate the elliptical paths.Alternatively, a first excitation frequency could be required togenerate depicted motion 100 a, and a second excitation frequency usedto generate motion 100 b. Yet other excitation frequencies provided bythe piezoelectric 22 could be used to change the direction of theelliptical motion to travel in an opposing direction.

[0167] Moreover, while the contacting portions 44 a, 44 b are shown atthe distal ends 36 of the vibrating element 26, the contacting portions44 could be at various locations and orientations on the vibratingelement 26. This is shown illustratively by engaging portion 44 n anddriven element 42 n, with the driven element 42 n rotating (e.g., todrive a gear) or translating along its longitudinal axis.

[0168] These aspects are further illustrated by the embodiment of FIG.62, which shows that the selected contacting portion 44 need not occurat the distal end 36 of the vibratory element 26. In FIG. 62 thevibratory element 26 has one or more selected contacting portions 44 elocated along the periphery of the element along the longitudinal lengthof the element. A second one or more selected contacting portions 44 fare located on an opposing surface of the vibratory element. Preferablythe selected contacting portions 44 comprise slightly raised areasextending above the surrounding portion of the vibratory element 26. Adriven element 42 such as a cylindrical shaft is placed in contact withthe contacting portions 44 e. In the depicted embodiment, the axes 25,45 of the vibratory element 26 and driven element 42 are aligned andcoplanar, but that need not be the case.

[0169] When the vibratory element 26 is excited at a first frequency,the contacting portions vibrate in an elliptical path 100 a causingmotion of the driven element 42 in a first direction. The contactingportion 44 e moves in an elliptical path opposite to that of contactingportion 44 f. To shift the motion of the driven element 42, thecontacting portion 44 f and driven element 42 are placed into contact.This can be achieved by moving one or both of the vibrating element 26and driven element 42. A rotation of the vibratory element 26 wouldsuffice in the illustrated embodiment. Thus, a single excitationfrequency could result in opposing directions of movement of the drivenelement 42. This embodiment also shows that the contact between thevibration element 26 and the driven element 42 can be a multiple pointcontact. It is not limited to a single point contact. This also allows,for example, the use of only one bearing pressing a driven rod 42 at twoto four points against the vibration element 26. The increased number ofcontacting portions 44 can increase the frictional engagement with thedriven element 42 and allow a greater power to be exerted on the drivenelement 42, and thus allow a greater power to be exerted by the drivenelement 42.

[0170] Alternatively, more than one driven element 42 could be placed incontact with differing portions 44 of the vibratory element 26,achieving different motions for each driven object. Moreover, thevibratory element 26 could be urged against a stationary surface and byselecting various contacting portions 44 (e.g., 44 e, or 44 f), move thevibratory element and any object connected to the vibratory element invarious directions over the surface.

[0171] Preloaded Motor Configurations

[0172] It is advantageous in many cases to use multilayer piezoelectricelements 22. These elements 22 are preferably of rectangularcross-sectional shape, but other shapes could be use such as square,circular, or other shapes. The piezoelectric elements 22 have layers ofpiezoelectric material with printed electrodes that are stacked on topof each other. Often many piezoelectric components are made at the sametime by producing a large stacked plate that is pressed and cut to formmany single piezoelectric elements.

[0173] As a result of this manufacturing method, the mechanical outputareas of the piezoelectric are typically parallel to the electrodelayers and are also flat. In order to use multilayer piezoelectricelements, a mechanical preload is often applied. This increases thelifetime of the piezoelectric by preventing delamination under dynamicmovement of the piezoelectric element, and it also optimizes the contactbetween the piezoelectric element 22 and the resonator 24 in which it ismounted. As a result, mechanical motion generated by the piezoelectricelement 22 is efficiently transferred through the contact zone to theresonator.

[0174] There are different methods to generate the preload. A resonator24 can be used that has two parts. A spring is used to generate thepreload by inserting a piezoelectric element 22 and the compressedspring between the two parts of the resonator which are then welded orotherwise fastened together. This way, a permanent preload is generated.

[0175] An alternative way to generate the preload is shown in FIG. 1,where the preload is preferably achieved by having the resonator 24exert a pressure on the piezoelectric element 22. The compressionensures that the vibrations of the piezoelectric element 22 aretransferred to the resonator 26 and selected contacting portion 44. Thecompression also avoids at least some damage to the piezoelectricelement 22 when high voltages are applied. The pressure is equal to theaxial force on the piezoelectric element 22 divided by the area overwhich the force acts. This area is the contact area between thepiezoelectric element 22 and the abutting portions of the resonator 26.Because the contact area can be difficult to measure, it is morestraightforward to use the force rather than the pressure as acharacterizing parameter.

[0176] The force exerted on the piezoelectric element 22 when no currentis passed through the piezoelectric element 22 includes: a staticpre-load equal to the axial force in the sidewalls 29 counteracting thepreload and a load component from the contact force arising from thecontact surface 44 being urged against the driven object 42. All ofthese forces fluctuate when a fluctuating current is passed through thepiezoelectric element 22.

[0177] The piezoelectric element 22 can be aligned so that the preloadon the piezoelectric element 22 is in the most active direction of thepiezoelectric element 22. While this is not necessary for the vibratorymotor 26 to operate, this configuration results in the highestefficiency. Preferably, for the beam-type vibratory element 26 depictedin FIG. 1, the greatest motion occurs in the line 3-3 direction that ispreferably aligned with the longitudinal axis 25.

[0178] Methods of producing a preload on the piezoelectric element 22that are described herein include: (1) clamping the piezoelectricelement 22 in the resonator 24 with a threaded fastener or othercompressive mechanism; (2) using force to press the piezoelectricelement 22 into a hole in the motor body in a manner similar to pressfitting of shafts; and (3) combinations thereof. Other preloadmechanisms can be used. The following disclosure expands on the threadedfasteners described thus far, and then discusses some press-fitmechanisms and methods. A wedge-based method and some variations on theabove methods concludes the discussion.

[0179] Threaded Preload Device & Method: FIGS. 1 and 5 illustrate athreaded fastener preload method and apparatus that is further describedbelow. The resonator element 26 is configured so that a hole, cavity oropening 28 is formed to accommodate the piezoelectric element 22. Theresonator can have various shapes, for example cross-sections that areround, square, rectangular, or polyhedral. The opening 28 is larger thanthe piezoelectric element 22 in all dimensions. A threaded fastener 32extends through a hole in a stationary object in order to allow thedistal end of the fastener 32 to press the piezoelectric element 22against the resonator 24. The threaded fastener 32 advantageously passesthrough a threaded hole in the resonator to directly abut the plate 34that is urged against the piezoelectric element 22.

[0180] Once the parts are assembled, a preload can be achieved in thepiezoelectric element 22 by tightening the threaded fastener 32. Thepreload can be approximately calculated by tightening the fastener 32 toa known torque. The threaded fastener 32 need not be aligned with thelongitudinal axis of the piezoelectric 22, but can be offset in avariety of ways so that tightening the threaded fastener urges twobodies toward each other to compress the piezoelectric element 22. Avariety of other mechanisms can be used to place the piezoelectricelement 22 in compression. Other preloading mechanisms are discussedlater.

[0181] Uni-Axially-Stressed, Press-Fit Preload Device & Method: Severalaspects of the press-fit of the piezoelectric element 22 are describedwith respect to FIG. 7a. The resonator 24 is configured so that a holeor opening 28 for the piezoelectric element 22 is formed in theresonator, with sidewalls 29 defining the sides of the opening. Theopening 28 is slightly smaller in the axial direction of thepiezoelectric element 22 than the combined length of the piezoelectricelement 22 and any other elements to be pressed into the opening 28. Therequired interference between the resonator 24 and the parts to bepressed into the opening 28 depends on the geometry and dimensions ofall parts and also the elastic strain of the material from which theresonator 24 is made.

[0182] Referring to FIG. 7b, the piezoelectric element 22 can be presseddirectly into the resonator 24.

[0183] This press-fit can be made easier by providing a tapered surface82 which places an inclined contact area between the abutting edges ofat least one of the piezoelectric element 22 and an end wall of theresonator 24 at the mating portion of opening 28. The inclined surface82 avoids an offset, abutting-type of interference, and provides asliding interference at the start of the press-fit. An improved way toachieve this press-fit is described later. This preload mechanism andmethod produces large shear stresses on the contacting surfaces of thepiezoelectric element 22. Because the piezoelectric material is brittle,the stresses can result in cracking of the piezoelectric element 22. Toavoid these shear stresses and protect the piezoelectric element 22, itis also possible to simultaneously press in a piezoelectric element 22sandwiched between two strips of a less brittle material 84 (FIG. 7a)such as a metal, preferably steel. The strips of material 84 can have avariety of shapes suitable to the configuration of the piezoelectricelement 22 and the vibrational element 26. The protective cap 84 canalso advantageously be used to guide the piezoelectric element 22 intothe opening 28, thereby eliminating the need for tapering of any parts.One of the strips of material 84 can advantageously comprise the end 50b of spring 50 that connects the vibrating element 26 to the base 52.

[0184] When the piezoelectric element 22 and any end protectors 84 areinserted into the opening 28, the sidewalls 29 are stretched toaccommodate the longer length element 22 and any end protectors 84. Thestretched sidewalls 29 act as springs and maintain the preload on thepiezoelectric element 22. Ideally, the preload on the piezoelectricelement 22 could be specified by knowing the cross-sectional dimensionsof the sidewalls 29 and fixing an interference that results in anelastic strain in the sidewalls 29 and therefore known stress andpreloads in the sidewalls. The preload is then this stress multiplied bythe combined cross-sectional area of the sidewalls 29.

[0185] Unfortunately, this method may not be practical because therequired interference for small vibratory elements 26 of an inch or lessin length is likely to be too small, on the order of 0.0001 inches,which is beyond a tolerance currently obtainable by traditionalmachining processes at a reasonable cost. Larger vibratory elements mayhave larger preloads that require larger dimensions, but the accuracyneeded to achieve those dimensions is likely to require similarly smalltolerances and thus also require expensive machining or polishing. Thisarises in part because small variances in the interference would resultin great differences in the preload when the sidewalls 29 are in theelastic portion of the stress-strain curve and act as a spring as thepiezoelectric element 22 expands and contracts.

[0186] Because of these disadvantages, it is desirable to make theinterference between the length of the vibratory element 26 and theopening 28 sufficiently large so that the sidewalls 29 forming theopening 28 are stressed beyond their yield strength but below theirultimate tensile strength, and a sufficient amount below their fatiguestrength to provide an acceptable product life. When stressed beyond theyield strength, the sidewalls 29 provide a relatively constant preloadeven though the dimensions of the opening 28, or the piezoelectricelement 22 or the end protectors 84 may vary. This allows loosermanufacturing tolerances and results in greatly simplified manufacturingand significantly lower costs.

[0187] The plastic portion of the stress-strain curve from yield up tothe point where necking of the sidewalls 29 begins, can be used toachieve the desired preload. The usable portion of the strain occurringafter yield and before necking is at least ten times larger than theelastic portion in strain. This is believed to apply to all non-ferrousmetals, which are the preferred material for the resonator 24, withaluminum being the most preferred non-ferrous metal. Ferrous metals andsome non-metallic materials could also be used in other embodiments.

[0188] This method significantly loosens the required tolerance on theinterference fit between the vibratory element 26 and the opening 28.Further, the slope of the stress-strain curve above yield is much lessthan that of the elastic portion. Thus, the preload will also not dependso greatly on the amount of interference. Using this method and design,the preload can be estimated as the yield strength multiplied by thecombined cross-sectional area of the sidewalls 29 for the depictedconfiguration. Other configurations will require other calculations, butsuch calculations are known to one skilled in the art and are thus notdescribed in detail herein.

[0189] The press-fit method has several advantages over using threadedfasteners to preload the piezoelectric element 22. The performance ofpress-fit piezoelectric elements 22 is more repeatable because thepreload and contact area are better defined. Furthermore, the preload ofa press-fit piezoelectric elements 22 can be easily calculated and doesnot depend heavily on manufacturing tolerances. The press-fit methodalso reduces the number of total motor parts, because it does notrequire the spring 50 to be clamped separately to the vibrating element50 as the end 50 b can be used to press-fit the piezoelectric elements22 into the opening 28. In addition, assembly of the vibratory element26 is made easier by eliminating the need for a threaded fastener 32 anduncertainties in its tightening and loosening during vibration.Eliminating the threaded fastener 32 also eliminates the need for atapped hole and thus reduces manufacturing costs.

[0190] The vibratory element 26 shown in FIG. 1 has two straightsidewalls 29 on opposing sides of the opening 28. The sidewalls couldcomprise different configurations, such as beams at each corner. But inthese configurations the sidewalls 29 are straight and generallyparallel to the longitudinal axis of the piezoelectric element 22. Thatresults in sidewalls that remain primarily in uni-axial tension duringpreloading and operation of the piezoelectric element 22.

[0191] Curved-Beam Configurations For Press-Fit Preloads: Alternativeconfigurations having sidewalls that curve away from the piezoelectricelement and from each other can provide a number of advantages. Thepress-fit operation for these two general types of vibratory elements 26does not differ. But the resulting advantages of the basic configurationcan differ significantly, as discussed below. The source of the problemand some partial solutions are discussed first, and then the advantagesof curved sidewalls 29 are discussed relative to FIG. 8.

[0192] Referring to FIG. 7, the preload on the piezoelectric element 22is estimated as the yield strength of the material multiplied by thecombined cross-sectional area of the sidewalls 29, because the sidewallsare stressed in uniaxial tension. This means that the entirecross-section of a sidewall 29 experiences the same stress. If thesidewalls 29 have the same cross-sectional area and the piezoelectricelement 22 is pressed so its longitudinal axis coincides with thelongitudinal axis 25 of the vibratory element 26, then the sidewalls 29also experience the same force and the same stress. If the sidewalls 29are of constant cross-sectional area, the stress is also constant overthe length of the sidewalls measured along the longitudinal axis 25 ofthe vibratory element.

[0193] The piezoelectric element 22 must move the resonator 24 andselected driving portion 44 to achieve a sufficient physicaldisplacement to move the driven element 42. Because the sidewalls 29 actas springs to preload the piezoelectric element 22, a portion of thepreload must be overcome in order to extend the vibratory element 26 andmove the selected contacting portion. If the stiffness of the sidewalls29 is too large, too much of the energy of the piezoelectric element 22may be expended in pushing against the sidewalls 29 and the amount ofvibratory energy that is transferred to movement of the selectedcontacting portion 44 and driven element 42 thus is reduced.

[0194] For a small vibratory element 26 of about one inch (2.54 cm) orless in length, the maximum forces on the piezoelectric element 22 andthe desire to have the sidewalls 29 in the yield region result inconfiguring the sidewalls 29 to have a thickness on the order of 0.01inches (0.25 mm). At such dimensions, or smaller, inaccuracies inmanufacturing parts of aluminum can result in significant percentagedifferences in the thickness of sidewalls 29. This leads to largerstresses in areas with smaller cross-sections and ultimately aconcentration of stresses and strains in the smallest cross-sectionalarea. This concentration of stresses and strains over a short section ofthe sidewall 29 increases the chance of necking in this region duringthe press-fit operation.

[0195] Necking is undesirable for several reasons. Because all fartherstrain in the sidewalls 29 produced by handling, temperature changes, oroperation of the motor assembly 20 will be concentrated in the veryshort necked region, the large stresses and strains in the necked regioncan lead to fatigue failure during operation of the motor assembly 20.Moreover, the necking can result in the geometry and therefore thevibrations of the sidewall 29 and vibratory element 26 to change andalter the performance of the motor assembly 20.

[0196] Fatigue failure in vibratory elements 24 with sidewalls 29 inpredominantly uniaxial tension is a concern even when necking is notpresent. Because the sidewalls 29 are put into yield, the fatigue meanstress during motor operation is near the yield strength of thematerial. The amplitude of the stress is very small because thepiezoelectric element 22 produces deflections on the order of hundredsof nanometers as it operates at about 30 kHz-90 kHz. The highfrequencies result in very large cycles of operation, but at very smallamplitudes. Ferrous metals have a stress endurance limit such that thesemetals, if operated below this limit, do not suffer from fatiguefailure. An endurance limit for aluminum and other nonferrous metals hasnot been observed (at least not below 100 million cycles). There is aconcern that small stress amplitudes eventually may lead to fatiguefailure in these materials because the motors 20 are operated atfrequencies in the range of tens of kilohertz, and at this rate it doesnot take more than several hours for a motor to accumulate more than abillion stress amplitude cycles, albeit cycles of low amplitude.

[0197] Published fatigue data here is not available but fatigue failuresin such motors have been observed at more than one billion cyclesimplying that it is desirable to take steps against fatigue failure.Using a manufacturing process that produces sidewalls 29 with nearlyconstant cross-sectional dimensions will improve fatigue properties byallowing the entire sidewall 29 to absorb stresses and strains insteadof just one small area of the sidewall. Improving the surface finish ofthe sidewalls 29 also helps by reducing the number of crack initiationsites. Assuring that the sidewalls are equally stressed by giving themthe same cross-sectional area and taking care to center thepiezoelectric element 22 will also help avoid fatigue failure.

[0198] Referring now to FIG. 8, a vibratory element 26 p is shown thatcan be used with any of the motor assemblies 20 described herein. Thevibratory element 26 p has curved sidewalls 29 p, which are put in amore complicated state of stress, when the piezoelectric element 22 ispressed into opening 28 p in resonator 26 p. The opening 28 p hasopposing flat portions 31 to abut the ends of the piezoelectric element22, and is configured to produce curved sidewalls 29 p. Thus the opening28 p is generally circular but with two opposing flats locatedorthogonal to an axis 25 p corresponding to the longitudinal axis of thepiezoelectric element 22. The remainder of the resonator 24 p can havevarious configurations suitable to the desired motion of and location ofthe selected contacting portion 44. Here the resonator 24 p is shownwith a rectangular configuration except for the opening 28 p defined bycurved sidewalls 29 p. The curved sidewalls advantageously have auniform cross section along the curved length, with the depictedconfiguration having a rectangular cross-section along the length of thecurved sidewalls. The curved sidewalls preferably have a uniform crosssection for a substantial portion of the length of the sidewall. As usedhere, that substantial length advantageously refers to more than halfthe length of the sidewall 29, and preferably refers to 75% of thelength of the sidewall 29, and ideally refers to over 90% of the lengthof the sidewall 29 between the end walls 31.

[0199] For curved sidewalls 29 p, the stress state can still beapproximated as uniaxial but the stress in the sidewalls is not uniformand is actually a combination of bending and axial stresses. Thesestresses can be determined using classical beam theory calculations.Alternatively, the deformations of the sidewalls can be approximated byfinite element methods or Castigliano's theorem.

[0200] In this embodiment, the sidewalls 29 are also advantageously putinto plastic deformation during the press-fit of the piezoelectricelement 22 and any protective plates 84 in order to make the preloadapproximately constant regardless of small differences in the amount ofthe interference fit. But the vibratory element 26 p has sidewalls 29 pthat are not uniformly stressed, and are instead stressed like a curvedbeam in bending. The curved configuration of the sidewalls 29 p alwaysresults in the maximum stress being located on the outside and insidesurfaces of the sidewalls 29 p, at the ends of the curved walls 29 pjoining the main body of the resonator 24. These stresses basicallyoccur where the curved walls 29 p join the remainder of the body of theresonator 24. These stresses occur on the inside of the walls 29 pforming the opening 28 p, and also on the outside of the walls 29 p. Thecurved walls result in four defined areas of maximum stress 86 on eachsidewall 29 p, two on the inside of the walls and two on the outside ofthe walls.

[0201] Significantly, this implies that these areas reach plasticdeformation first rather than having the entire cross-section ofsidewall 29 reach plastic deformation simultaneously when thepiezoelectric element 22 is press-fit into the opening 28 p. Thislocalized yielding can have advantageous results.

[0202] The vibratory element 26 p has several advantages over thevibratory element 26 of FIG. 7a. Because the sidewalls 29 p are curved,they can be much thicker than straight sidewalls 29 and still achievethe same preload on the piezoelectric element 22. This is better formanufacturing and better for the fatigue lifetime of the vibratoryelement 26 p. Thicker walls increase the fatigue lifetime because smallmaterial flaws and manufacturing errors will be proportionally smaller.Such material flaws and manufacturing errors are the most probablelocations of crack initiation leading to fatigue failure.

[0203] Further, in high cycle fatigue, most of the fatigue lifetime isspent in initiating the crack, and the thicker walls help reduce thatcrack initiation. Moreover, fatigue cracks start in the wall sectionsthat are under the highest stress. In the walls 29 p the locations ofmaximum stress are known as explained above, and that allows steps to betaken to reduce stress concentrations. For example, in order to reducethe stress concentrations in these high-stress areas it is preferablethat the sidewalls 29 p have fillets or rounded junctures (at points 86)with adjoining walls, on both the inside and outside of the walls 29 p,as shown in FIG. 8. Because the critical stress areas are known and canbe either reinforced or have stress-relieving steps applied to them, itis believed unnecessary with the vibratory element 26 p to require morethan a machined surface finish. The expense and effort of a polishedsurface is not believed necessary.

[0204] Additionally, necking is also not a severe problem with thevibratory elements 26 p because of the non-uniform stress distributionacross the thickness of the sidewalls 29 p. The vibratory element 26 palso has an advantage in that the spring constant of the sidewalls 29 p,the axial force divided by axial deflection, is lower compared to thesidewalls 26 of FIG. 7a. A lower spring constant allows thepiezoelectric element 22 to expend more energy in moving the drivenelement 42 rather than pushing against the preload spring formed bysidewalls 29, 29 p. For these reasons, it is advantageous to use curvedsidewalls 29 p rather than straight, uni-axial tension sidewalls 29. Thesidewalls 29 p are preferably of uniform curvature, and symmetric aboutthe portion of the longitudinal centerline 25 p extending through theopening 28 p. In comparison to straight sidewalls, curved sidewalls alsoallow the opening 28 to be dilated by a larger amount (elastically orplastically).

[0205] Wedging Preload Methods & Designs:

[0206] Referring to FIGS. 9-11, a method and apparatus using a wedgingeffect is described using a resonator of the configuration of FIG. 1.The resonator 24 is thus illustrated as a rectangular body with arectangular opening 28 both symmetrically aligned along longitudinalaxis 25. Other shapes could be used. The opening 24 is slightly largerthan the piezoelectric element 22 and any protective cap 84, measuredalong the longitudinal axis as reflected in FIG. 10. A slight press-fitis also acceptable. A hole 90 is placed through the resonator 24 at oneend of the opening 28. The hole 90 is shown here as being placed in theend of the resonator 24 opposite the driving end 44 (FIG. 1) andadjacent the end connected to spring 50 (FIG. 1).

[0207] As shown in FIGS. 10-11, a wedge 92 is forced into the hole 90sufficiently to deform the hole 92 and the adjacent end of the opening28. As illustrated, the hole and wedge are both cylindrical, and locatedadjacent an end of the opening 28, so as to cause a bulging along thelongitudinal axis into the opening 28 sufficient to compress thepiezoelectric element 22 within the opening 28. Basically, the wedgedistorts one wall of the opening 28 to place the piezoelectric intocompression. The intervening protective plate 34 (FIG. 1) could be usedon one or both ends of the piezoelectric element 22, or omitted.

[0208] Because the dimensions of the cylindrical hole and wedge can beclosely controlled and positioned on the resonator 24, and because thematerial properties of the parts are known and predictable, a precisedeformation of the opening 28 can be achieved. The distortion must besymmetrically achieved if the forces in sidewalls 29 are to be keptequal. But if an offset compression is desired in order to potentiallyskew the axis along which the force of the piezoelectric element 22 actsrelative to the resonator 24, then the hole 90 can be offset from thelongitudinal axis 25.

[0209] Referring to FIGS. 12, the hole need not be circular, but couldcomprise a rectangular slot, with the wedge 92 being correspondinglyconfigured to distort the hole 90 as needed to create the appropriatepreload. A wedge 92 with a rectangularly shaped cross-section, or withan elliptically shaped cross section, could be used. As the shape of thewedge 92 changes to increase the amount of deformed material, the forceneeded to insert the wedge 92 into the hole 90 increases.

[0210] As discussed later, there are advantages in some situations ifthe piezoelectric element 22 applies its force along an axis eitherparallel to but offset from the longitudinal axis 25 of the resonator24, or at a skew angle relative to that longitudinal axis 25. FIGS.13-16 illustrate several ways to achieve this offset and skewing of therelative longitudinal axes of piezoelectric element 22 and resonator 24.Another variation is discussed later regarding FIG. 53.

[0211]FIG. 13 shows the piezoelectric element 22 offset within theopening 28 so the centerline 95 of the longitudinal axis of thepiezoelectric element 22 is laterally offset from the centerline of theaxis 25 of resonator 24. The offset can be above, below, or to eitherside of the centerline 25, depending on the desired motion of theselected contacting portion 44.

[0212]FIG. 14 shows a small, hardened insert 94 interposed between oneend of the piezoelectric element 22 and the adjacent wall of the opening28. A hardened steel ball or a small disk could be used, but it must besized or shaped relative to the abutting portions of the resonator sothat no unacceptable deformation of the insert 94 occurs under drivingforces applied by the piezoelectric element 22. In this embodiment aprotective cap 34 is preferably used in order to avoid localized forceson the more brittle piezoelectric element 22 that might damage thepiezoelectric. The location of the insert 94 can be above, below, or toeither side of the centerline 25, depending on the desired motion of theselected contacting portion 44. More than one insert can be used.

[0213]FIG. 15 shows the opening 28 and piezoelectric element 22 alignedalong axis 95 of the piezoelectric element 22, but both located at askew angle relative to longitudinal axis 25 of the resonator 24. Thisresults in an asymmetrical mounting of the piezoelectric element 25relative to the centerline of the resonator 24. The amount of skewing ofthe relative axes of the piezoelectric element 22 and the resonator 24will depend on the desired motion of the selected contacting portion 44.This configuration has the disadvantage of creating sidewalls 29 havinga varying cross-section. But given the present disclosure, it ispossible for one skilled in the art to mount the piezoelectric element22 at a skew angle to the longitudinal axis 25 of the resonator 24 andthe vibratory element 26. Placing small inserts 94 on opposing ends ofthe piezoelectric element 22 (see FIG. 16), and on opposing sides of thelongitudinal axis 25, could also achieve a skew axis of thepiezoelectric element 22 relative to axis 25. Various combinations ofthe above, and later described mounting systems can be used.

[0214] Mounting Of Vibratory Elements & Driven Elements

[0215] Given the present disclosure, a variety of mountingconfigurations are possible for the vibrating element 26 and resilientmounting system 50. The mounting configuration is often determined bythe location of the selected driving portion 44 and the mating engagingportion of the driven element 42, and the required motion of thoseelements.

[0216] Referring to FIG. 17, the vibratory element 26 is mounted to adistal end of a rigid beam 102 that is pivotally mounted at a pivotedend to rotate about pivot point 104. The vibratory element 26 has aselected contacting portion 44 resiliently urged against the drivenelement 42. The selected contacting portion 44 is shown inward of thedistal end 36 of the vibratory element 26 to reiterate that the locationof the selected contacting portion 44 can be at various locations on thevibratory element 26. The same applies for the other mountingconfigurations discussed herein.

[0217] As illustrated in FIG. 17, spring 50 resiliently urges the partsto maintain sufficient contact during the desired portion of the motionto move the driven element. The spring 50 may take various forms and beconnected in a variety of ways. The driven object 42 can have a varietyof shapes, or motions. Useful forms of driven objects 42 comprise one ofa rod, a ball or a wheel that is located at a distal end of thevibratory element 26. The driven element 42 needs to be appropriatelysupported to allow its intended motion, and that support is not shownhere as the motion can vary according to design.

[0218]FIG. 18 shows an arrangement similar to FIG. 17, but with thelocation of the resilient force altered so that it is exerted on thedistal end of the pivoted rigid element 102 and pulls the vibratoryelement 26 into contact with the driven element 42 rather than pushingit into contact. The spring 50 applying the resilient forceadvantageously applies its urging force along an axis aligned with thelongitudinal axis 25 of the vibratory element 26, but that is optional.

[0219]FIG. 19 shows an arrangement similar to FIGS. 17-18, but with thelocation of the resilient force altered so that it is exerted adjacentto the pivoted end of rigid element 102. The location of the resilientforce, such as applied by spring 50, can affect the displacement of thespring. When the spring 50 is located nearer the pivot point 104, thespring 50 does not move much because the effective moment arm betweenthe pivot point and the connection to the spring is less.

[0220] If the vibratory element 26 is rigidly mounted, configurationssimilar to those described herein can be used to resiliently urge thedriven element 42 to maintain sufficient contact with the fixedlymounted vibratory element 26 to achieve the desired movement of thedriven element.

[0221]FIG. 20 shows one advantageous mounting configuration that uses aflat strip of spring metal for the spring 50. The spring 50 has a firstend 50 a mounted to a base 52, and an opposing end 50 b connected to thevibratory element 26. A first leg of the spring 50 containing end 50 ais parallel to the longitudinal axis 25 of the vibratory element 26,with the second leg of the spring being bent at about a right angle. Thedistal end of the vibratory element 26 is resiliently urged against thedriven element 42. The driven element 42 can in principle have anysufficiently smooth shape, but readily useful forms of driven objects 42comprise one of a rod, a ball or a wheel that is located at a distal endof the vibratory element 26. The driven element 42 needs to beappropriately supported to allow its intended motion, and that supportis not shown here as the motion can vary according to design.

[0222]FIG. 21 shows a straight, leaf spring 50 a having one end rigidlymounted to base 52, with an opposing distal end 50 b mounted to thevibratory element 26. The distal end of the vibratory element 26 isurged by the spring 50 against the driven element 42. Other shapes ofsprings 50 are possible.

[0223]FIG. 22 shows a vibratory element 26 having a first end pivotedabout pivot 106 and an opposing distal end resiliently urged by spring50 against a driven element 42. The selected contacting portion 44 isintermediate the pivot point 106 and the connection of spring 50 alongthe longitudinal axis 25, and is on an opposing side of the axis 25 asis the spring 50 and pivot 106. But various locations of the selectedcontacting portion 44 relative along the axis 25 are possible, dependingon the desired motion and the configuration of the parts.

[0224] There is thus provided a method and apparatus for generating atleast two components of motion at the selected contacting portion 44.These two motion components have mutually different directions, witheach component oscillating when the piezoelectric element 22 is excitedat a predefined frequency, and with the two components having mutuallydifferent phases. These two motion components are shaped so as to createan elliptical motion 100 along a desired orientation, by configuring thevibratory element 26, its suspension 50, or both. There is alsoadvantageously provided a method and apparatus by which the same orother contacting portions 44 create suitable ellipses 100 at variousexcitation frequencies of the piezoelectric element 22, resulting inmutually different macroscopic motions of the driven body 42 engagingone or more of the selected contacting portions(s) 44.

[0225] In one embodiment, the vibration element 26 is attached to thebase 52 with a spring-like element 50, wherein the spring can be of thebending, torsion, pneumatic, elastomeric, or any other type. The springcould for example be made from portions of an electronic circuit board,which has advantages in manufacturing. The spring constant orflexibility of the spring can be adjusted to compensate for wear in thecontact area between contacting portion 44 and the engaging portion ofthe driven element 42, and can also compensate for productioninaccuracies. For instance, high compliance of the spring 50 results insmall variations in the resilient contact force the contacting portion44 exerts on the driven element 42 despite relatively large deflectionsof the contacting portion 44.

[0226] The spring 50 can be attached to the vibration element 26 in manydifferent ways. In one embodiment, the vibration element 26 contains anopening 28 with a dimension slightly smaller than the sum of acorresponding dimension of the undeformed piezoelectric element 22 andthe thickness of the spring 50. Inserting the spring 50 and thepiezoelectric element 22 into the opening 28 causes the opening toexpand, thus creating a press-fit that functionally connects saidvibration element to the spring and the piezoelectric element. Inanother embodiment, the vibration element contains an opening, such as aslot, into which an end of the spring can be pressed, glued, screwed, orotherwise fastened. The slot can be oriented in any preferable way. Inone embodiment, the slot is oriented perpendicular to the longitudinalaxis 25 of the vibrating element 26. In another variation, it isoriented parallel thereto.

[0227] In addition to connecting the vibration element 26 to the housingor base 52, the spring-like element 50 can also be a functionalextension of the vibration element 26. With proper adjustments, thespring 50 can isolate the vibrations of the vibration element 26functionally from the housing 52. Also, the spring 50 can influence thedynamic behavior of the vibration element 26 in order to enhance theperformance of the vibration element 26 through amplification or otherdynamic effects. For instance, if the spring 50 has axes of symmetrywhich are different than, or offset to those of, the axes of symmetry ofthe vibration element 26, then the assembly of the piezoelectric element22, vibration element 26 and spring 50 becomes dynamically asymmetricalresulting in a coupling of what were formerly independent modes ofvibration.

[0228] In a further embodiment, the vibrating element 26 can be attacheddirectly to the housing or base 52. It is preferable if the housing orbase 52 functionally isolates the vibrations of the vibrating element26. In this embodiment, the housing itself must exert the resilientforce that presses the vibrating element 22 against the moving element42. It is preferable if the design of the housing or base 52 provides amechanism to adjust the contact force and to compensate for motor wear.A screw in a slot to adjustably position the vibratory element 26relative to the driven element 42 is one example.

[0229] In yet another embodiment, the vibration element 26 is rigidlyconnected to the housing 52, and the driven element 42 is resilientlyurged against the vibrating element 26 by the bearings in or on whichthe moving element is supported. For this purpose, it is preferable ifthe support contains some sort of spring or other compressible medium toprovide a resilient force to urge the parts into contact. In thissituation, the motor assembly 20 could also mounted in a position sothat gravity acting on the driven element 42 may provide the necessaryresilient force.

[0230] Locating Driving & Driven Elements

[0231] Referring to FIGS. 23-36, various configurations are shown formounting the vibratory element 26 relative to the driven element 42.These figures are schematically shown, and omit the mounting systems ofthe parts that allow the desired motion and that maintain the parts insufficient contact for the intended use. For illustration the drivenobject 42 is shown as a rod with a cylindrical cross section, but itcould be a ball, a wheel, a rod, a bar, a gear or something else. Thevibratory element 26 needs to be urged against the driven object 42 witha certain force and angle to achieve the contact needed to cause motion.This can be achieved through the mounting mechanisms described earlieror apparent to those skilled in the art given the present disclosure.The mechanism causing that resilient contact is not shown. Also notshown is the mounting arrangement that allows the desired movement ofthe driven part 42 as that will vary with the particular design. Thefollowing arrangements are only examples. Others are possible but arenot described since it is not possible to cover all of them.Combinations of these arrangements are possible as well.

[0232] Single Vibratory Element Configurations: FIGS. 23-26 showconfigurations using a single vibratory element 26. In FIG. 23, thevibratory element 26 is above the driven element 42, with at least oneof the elements 26, 42 being resiliently urged to maintain the selecteddriving portion 44 in sufficient contact with the selected engagingportion of driven element 42 to achieve the desired motion. Thelongitudinal axes of the vibratory element 26 and the driven element 42are perpendicular to each other, but they could be at variousintermediate angles. The contact portion 44 is inward of the distal end36, but could be at an location along the length of the vibratoryelement 26 achieving the desired motion at a selected amplitude. Thecontact portion 44 is thus advantageously selected to occur at alocation having the desired elliptical motion 100. The motion 100 isshown generally aligned with the axis 25 of the vibratory element 26,which will cause rotation of the driven element 42 about axis 45. Butthat need not be the case, as it could be in a plane orthogonal to axis25 to cause translation along axis 45, or at orientations in between,depending on the desired motion and the design of the components. Asused herein, an alignment of about 0-5 degrees will be considered to bealigned.

[0233]FIG. 24 shows the longitudinal axis 25 vertically offset from andperpendicular to the axis 45 of the driven element. Various intermediateangles of inclination are possible. The selected contact portion 44 isat the distal end 36, at a lower peripheral edge of the vibratoryelement 26. This arrangement lends itself to producing rotation of thedriven element 42 about axis 45, or translation along that axis, orcombinations of those motions.

[0234] In FIGS. 25-26, the longitudinal axes 25, 45 are coplanar andinclined relative to each other at an angle α as discussed relative toangle α of FIG. 1. The selected contact portion 44 is at the distal end36, at a lower peripheral edge of the vibratory element 26. Thisarrangement lends itself to producing translation of the driven element42 along axis 45, or rotation about that axis, or combinations of thosemotions. Referring to FIG. 26, the axes 25, 45 are shown as coplanar,but they need not be so and could intersect at skew angles.

[0235] Multiple Vibratory Element Configurations: Configurations usingmultiple vibratory elements 26 that cooperate to move the driven element42 are shown in FIGS. 27-42. The use of multiple vibratory elements 26has the advantage of providing more locations of support to the drivenelement 42 so that some of the bearings may be omitted. Thus, costsavings and friction reduction that typically comes with low costbearings or bushings are achieved. In some applications, it can beenough to suspend the driven element 42 entirely using vibratoryelements 26 without the need for additional bearings. The vibration ofthe contacting portion of the vibratory element 26 can provide a lowfriction support, and an elliptical motion of the supporting portion ofthe vibratory element 26 is not necessary for this low friction supportapplication.

[0236] Further, the use of multiple vibratory elements 26 canaccordingly multiply the force, and/or the speed with which the drivenelement 42 is moved. A single, common excitation signal could beprovided to each of the vibratory elements 26 in order to simplify theelectrical system, or separate signals could be provided to causedifferent simultaneous motions of the driven element 42.

[0237] In the following, configurations with a specific number ofvibratory elements 26 are described. Given the disclosures therein, avariety of other mounting configurations can be configured that usemultiple vibratory elements 26 to restrain various degrees of freedom ofthe driven element 42.

[0238] Double Vibratory Element Configurations: Configurations usingspecifically two vibratory elements 26 and a single driven element 42are shown in FIGS. 27-36. In FIG. 27 there are two vibratory elements 26resiliently urged against opposing sides of driven element 42. The twovibratory elements 26 have axes 25 perpendicular to the longitudinalaxis 45 of driven element 42, and on opposing sides of that axis 45. Theselected contacting portion 44 of each vibratory element 26 a, 26 b ispreferably intermediate the distal ends of the vibratory elements, butthat need not be the case as the contacting portion 44 could be atdistal end 36. The axes 25 of the vibratory elements 26 can be paralleland coplanar, but they do not have to be either parallel or coplanar.This arrangement lends itself to producing translation of the drivenelement 42 along its longitudinal axis 45, or rotation about that axis,or combinations of those motions.

[0239]FIG. 28 shows two vibratory elements 26 resiliently urged againsta common side of driven element 42. The two vibratory elements 26 haveaxes 25 perpendicular to the longitudinal axis 45 of driven element 42,but the axes 25 could be inclined to axis 45. The axes 25 of thevibratory elements 26 can be coplanar, but need not be so. The contactportions 45 are at distal edges of each face 36. The contact portion 44is at an angle 45 degrees from the horizontal plane in which the axis 45is shows as being located, but on opposing sides of that plane. Thisconfiguration lends itself to producing translation of the drivenelement 42 along its longitudinal axis 45, or rotation about that axis,or combinations of those motions.

[0240]FIG. 29 shows a configuration similar to FIG. 28 except that thevibratory elements 26 face each other and are located on opposing sidesof the driven element 42 relative to the vertical axis.

[0241]FIG. 30 shows a configuration similar to FIG. 24, except there aretwo vibratory elements 26 on opposing sides of the driven element 26, ona common axis 25. The longitudinal axes 25 of each vibration element 26need not coincide, but could be coplanar and skewed relative to eachother.

[0242]FIG. 31 has two vibratory elements 26 on opposing sides of thedriven element 42, with the elements 26 facing each other but orientedat inclined angles α, β, respectively, relative to a plane through thelongitudinal axis 45 of driven element 42. The angles α, β are shown sothe axes 25 of each vibratory element 26 are parallel, but they need notbe parallel. The angles preferably cause the longitudinal axes 25 tointersect the longitudinal axis 45 of the driven element 42, but neednot do so. The selected contact portion 44 is at the distal end 36 ofeach vibratory element 26.

[0243]FIG. 32 has two vibratory elements 26 on opposing sides of thedriven element 42, with the elements 26 facing the same direction andoriented at inclined angles α, β, respectively, relative to a planethrough the longitudinal axis 45 of driven element 42. The angles α, βare such that the longitudinal axes 25 preferably intersect longitudinalaxis 45 of the driven element 42, but need not do so. The selectedcontact portion 44 is at the distal end 36 of each vibratory element 26.

[0244]FIG. 33 has two vibratory elements 26 on the same side of thedriven element 42, with the elements 26 facing the same direction andorientated at inclined angles α, β, respectively, relative to a planethrough the longitudinal axis 45 of driven element 42. The angles α, βare such that the longitudinal axes 25 preferably intersect longitudinalaxis 45 of the driven element 42, but need not do so. The axes 25 neednot lie in the same plane, but preferably do so. The selected contactportion 44 is at the distal end 36 of each vibratory element 26.

[0245]FIG. 34 has two vibratory elements 26 on the same side of thedriven element 42, with the elements 26 facing each other and orientedat inclined angles α, β, respectively, relative to a plane through thelongitudinal axis 45 of driven element 42. The angles α, β are such thatthe longitudinal axes 25 preferably intersect longitudinal axis 45 ofthe driven element 42, but need not do so. The axes 25 need not lie inthe same plane, but preferably do so. The selected contact portion 44 isat the distal end 36 of each vibratory element 26.

[0246] FIGS. 35-36 show a configuration with two vibratory elements 26on opposing sides of the driven element 42, with the elements 26 facingthe same direction and orientated at inclined angles α, β, respectively,relative to a plane through the longitudinal axis 45 of driven element42. The angles α, β are such that the longitudinal axes 25 preferablyintersect longitudinal axis 45 of the driven element 42, but need not doso. The axes 25 need not lie in the same plane, but preferably do so.Advantageously, the axes 25 intersect at a common location on axis 45,with the engaging portions 44 being in the same plane orthogonal to axis45.

[0247] In this configuration, the selected contact portion 44 is at thedistal end 36 of each vibratory element 26. The selected contactportions 44 of each element 26 are configured to have a shape matingwith the shape of the engaged portion of driven element 42. Here, thecircular cross-section of rod 42 results in a convex curved surface forthe selected contacting portions 44. This curved engagement results inthe vibratory elements 26 providing a support for the driven element 42that restrains motion except for translation along axis 45. If thecontacting portion 44 has a small engaging surface along the length ofaxis 45, then the driven element 42 will rock about the engagingportions 44. If the contacting portion 44 has an engaging surface with asufficient length along the length of axis 45, then the driven element42 can be supported without rocking about the engaging portions 44. Thisconfiguration can simplify the mounting of the driven element 42 byallowing the vibratory elements 26 to also act as bearings by clampingthe rod between the tips of two vibratory elements 26.

[0248] Triple Vibratory Element Configurations:

[0249] FIGS. 37-40 show configurations using three vibratory elements 26a, 26 b and 26 c, with the letters a, b, and c being associated with thevarious corresponding parts of the first, second and third vibratoryelements, respectively. FIG. 37 shows two vibratory elements 26 a, 26 bas described in FIG. 27, each of which is resiliently urged againstopposing sides of driven element 42. The two vibratory elements 26 a, 26b each have axes 25 perpendicular to the longitudinal axis of drivenelement 45, and on opposing sides of that axis 45. The selectedcontacting portion 44 a, 44 b of each vibratory element 26 a, 26 b ispreferably intermediate the distal ends of the vibratory elements, butthat need not be the case as the contacting portion 44 could be atdistal end 36. A third vibratory element 26 c is located on an opposingside of the driven element 42 with its selected contacting portion 44 cintermediate, and preferably equally between, the contacting portions 44a, 44 b along an axis between 44 a and 44 b. The driven element 42 hasits longitudinal axis along the z axial direction. Preferably, the firstand second vibratory elements 26 a, 26 b contact the driven element 42at the 12 and 6 o'clock positions, with the third vibratory element 26 ccontacting the driven element 42 at the 3 o'clock position. Othercontact locations are possible. The contacting portion 44 c ispreferably at a distal edge of the vibratory element 26 c, with thethird vibratory element 26 c being oriented at an angle α parallel tothe plane containing axes 25 a, 25 b. The axes 25 of the vibratoryelements 26 a, 26 b are preferably parallel and the axes 25 a, 25 b and25 c are preferably coplanar, but the various axes do not have to beeither parallel or coplanar. This configuration provides for translationand rotation of the driven element 42 along and about its longitudinalaxis 45, with the vibratory elements restraining translation in bothdirections along the y-axis, and in the +x direction, but allowingmotion along the −x direction.

[0250]FIG. 38 shows the vibratory elements 26 with their longitudinalaxes 25 perpendicular to a radial axis extending in a plane orthogonalto the axis 45 of the driven element 42. The contacting portions 44 areillustrated as offset from distal ends 36, but that need not be thecase. The vibrating elements 26 are shown as equally spaced with anglesβ, γ, and α each being about 60 degrees, but the angles can vary. Theaxes 25 a, 25 b, 25 c are shown as coplanar, but they need not be so.The driven element 42 has its longitudinal axis along the z axialdirection. This arrangement allows the vibrating elements 26 to restraintranslation of the driven element 42 in both directions along the x-axisand y-axis.

[0251]FIG. 39 places two of the vibratory elements 26 a, 26 b on oneside of the driven element with axes 25 a, 25 b parallel to the x-axis,and with their respective contacting portions 44 a, 44 b engaging theperipheral portion of the driven element at corresponding locationsalong an axis parallel to the vertical y-axis. The contacting portionsare located at edges of the distal ends 36 a, 36 b. The axes 25 a, 25 bare parallel and coplanar, but need not be coplanar or parallel. Thethird vibratory element 26 c is on the opposing side of the drivenelement 42, with axis 25 c parallel to the y-axis. The axis 25 c ispreferably coplanar with axes 25 a, 25 b, but need not be so. The drivenelement 42 has its longitudinal axis along the z axial direction. Thisarrangement allows the vibratory elements 26 to restrain translation ofthe driven element 42 in both directions along the x-axis and y-axis.

[0252]FIG. 40 places two of the vibratory elements 26 a, 26 b on oneside of the driven element with axes 25 a, 25 b parallel to the x-axis,and with their respective contacting portions 44 a, 44 b engaging theperipheral portion of the driven element at corresponding locationsalong an axis parallel to the vertical y-axis. The axes 25 a, 25 b areparallel and coplanar, but need not be coplanar or parallel. The drivenelement 42 has its longitudinal axis along the z axial direction. Thethird vibratory element 26 c is on the opposing side of the drivenelement 42, with axis 25 c parallel to the x-axis, and coaxial with axis25 b. The contacting portions are located at edges of the distal ends 36a, 36 b, 36 c. This arrangement allows the vibratory elements 26 torestrain translation of the driven element 42 in both directions alongthe x-axis and y-axis, but does permit motion along one direction of askew axis at 45 degrees from the horizontal as shown in FIG. 40.

[0253] In the above configurations using multiple vibratory elements 26,each vibratory element is preferably activated at the same time as theother vibratory elements so that the vibratory elements cooperate toproduce the desired motion of the driven element 42. But the vibratoryelements 26 could be separately activated at different times or indifferent combinations or in different sequences in order to achieveseparate motions of the driven element.

[0254] Six Vibratory Elements:

[0255] FIGS. 41-42 show a configuration in which six vibratory elements26 a through 26 f are used to support a driven element 42 that canrotate and translate about its longitudinal axis 45. The vibratoryelements 26 each have one end attached to a ring 110 that encircles thedriven element 42, preferably in a plane orthogonal to the longitudinalaxis 45 of the driven element. The opposing distal end 36 a through 36 fof the vibratory elements 26 is pressed against driven element 42. Threeof the vibratory elements 26 extend toward the driven element 42 indirections opposite to the other three vibratory elements as best seenin FIG. 42. The relative position of each vibratory element 26 viewed inthe x-y plane orthogonal to the axis 45 of driven element 42 (FIG. 41),is determined through the angles α, β, γ, σ, ε, and ρ. These angles arepreferably 60 degrees in order to equally distribute the support anddriving forces, but the angles can be different from that. The vibratoryelements 26 advantageously have their longitudinal axes 25 intersectingthe longitudinal axis 45 of the driven element 42, but the axes 25 couldbe skewed so they do not intersect the axis 45. The angles between thevibratory elements 26 and the driven element 42 are defined by δ and φas shown in the drawing, and will vary depending on the dimensions ofthe various parts and on the orientation of the vibratory elements 26.The flexibility of the ring 110 helps to ensure that the vibrationelements 26 are pressed against the driven element 42. As a result therod is suspended at six points.

[0256] This configuration allows the vibratory elements 26 to supportthe driven element 42 so as to allow translation only along thelongitudinal axis 45 of the driven element 45 and to allow rotationabout that axis.

[0257] Motor Operating Principles

[0258] The following description helps understand the operation of theabove-described embodiments, and helps understand the variety of ways toimplement these embodiments and variations thereon.

[0259] The present motor uses only one piezoelectric element 22 with oneelectrical excitation signal to excite various modes of vibration of thevibration element 26. The motion of the contact portion 44 is determinedby these modes of vibration. In particular, the present motor achievesan elliptical movement of the contact portion 44 in a first directionfor a sinusoidal electrical excitation signal at a first frequency, andan elliptical movement of the contact portion 44 in a second directionfor a sinusoidal excitation signal at a second frequency, providing arequired force or amplitude of motion or speed at the contact portion44. Elliptical movements of the contact portion 44 in a third and moredirections for sinusoidal excitation signals at third and morefrequencies are known to be possible.

[0260] The motor assembly 20 is advantageously configured so that thecontact portion 44 traces the elliptical motion several tens of thousandtimes per second to make motor operation inaudible for humans and mostpet animals. During a selected segment of each elliptical cycle, thecontact portion 44 comes into contact with the engaging surface of thedriven object 42 where it exerts a frictional contact force thattransports the driven object 42 by a small amount into a correspondingdirection. The observed macroscopic motion of the driven object 42 isthe accumulation of all individual transportation steps.

[0261] While the bulk of this disclosure refers to a contact portion 44located at a distal end 36 of vibration element 26 and moving in a firstelliptical path 100 a causing the driven object 42 to be transported indirection of the driven object's longitudinal axis 45, and the sameselected contact portion 44 moving in a second elliptical path 100 bcausing transportation in an opposing direction (as in FIGS. 2 and 5),the first and second selected contacting portions 44 need not be thesame, need not be adjacent, and need not be located at a distal end 36.They need only be located on the same vibratory element 26. Further, thenumber of selected contacting portions 44 and the directions andorientations of respective elliptical paths 100 at each contactingportion can vary according to the particular design. There could bethree, or there could be more. There can thus be a plurality of selectedcontacting portions 44 on the vibratory element 26 moving in a pluralityof elliptical paths 100 in a plurality of directions.

[0262] Advantageously the desired motion of a selected contact portion44 is identified, whether it is in a single direction or multipledirections, and whether there is a single selected contact portion 44 orseveral contact portions 44, or combinations thereof. The motor assembly20 is then designed to achieve that motion. As often occurs, the designdoes not achieve perfection but instead achieves an acceptableapproximation of the desired motion. A number of the factors that can beused to configure the components of motor assembly 20 to achieve thatdesired motion are discussed below.

[0263] Generation of elliptical motion: If the piezoelectric element 22is excited with a sinusoidal electrical signal, it generates asinusoidal force and a sinusoidal displacement principally along itslongitudinal axis 95, shown in FIGS. 1-3 as being alongside longitudinalaxis 25 of the vibration element 26, or shown in FIG. 15 as being at anoblique angle to the longitudinal axis 25. Said force and displacementare then used to excite modes of vibration of the vibration element 26.The vibration element 26 is preferably configured so that at apredetermined excitation frequency at least two of its modes ofvibration are substantially excited. If a mode has only a uniform motioncomponent in the direction of the longitudinal axis 25, it is consideredto be a longitudinal mode. If the motion components of a mode lie in adirection perpendicular to the longitudinal axis 25, the mode isconsidered to be a bending mode. Further well known modes includetorsion and shear modes. A mixed mode is neither of these modes but canhave components of motion in, or rotating around, any of the directions25, 38 or 40. Each mode that is excited adds a sinusoidal motioncomponent to the motion of the contact portion 44. If at least two ofthese components of motion are non-parallel and mutually out of phase,the resulting motion of the contact portion 44 is known to beelliptical.

[0264] The bulk of this disclosure refers to a piezoelectric element 22that generates force and displacement principally along its longitudinalaxis 95, but a piezoelectric element having a different principaldirection, or a force and displacement-generating element other than apiezoelectric element, could be used.

[0265] Making use of elliptical motion: It is an advantage of thepresent invention over prior art motors that elliptical motions do nothave to be achieved exclusively with mutually perpendicular longitudinaland bending modes that are excited 90 degrees out of phase, but insteadthat the elliptical motion can be generated with at least two excitedmodes that can be mutually oblique and have a phase difference that canbe substantially different from 90 degrees. In this case, the contactportion 44 traces an ellipse 100 whose semi-axes are not necessarilyaligned with any of the directions 25, 38 or 40, thus making itadvantageous for the vibration element 26 to be mounted at an obliqueangle to the driven object 42. That is, the longitudinal axis 25 ispreferably inclined to the vibration element 26 at an angle α (FIG. 1),which will vary with the particular design and components involved.Oblique mounting of the vibration element 26 rotates the ellipse 100with respect to the driven object 42. Associated with this rotation, acoordinate transformation is formulated elsewhere that exposes thebeneficial and enhancing effects of this rotation on relative phaseshifts between components of motions that generate the elliptical path100.

[0266] While the elliptical motion 100 of the selected contactingportion 44 is achieved even if the selected contacting portion 44 is notengaged with the driven element 42, in order to achieve useful motionthe contact portion 44 of vibration element 26 is placed in physicalcontact with the engaging surface of the driven object 42 during acertain portion of each elliptical cycle 100. This portion preferablyremains the same for each subsequent cycle. During each engagement, thevibration element 26 exerts frictional forces on the driven object 42.These forces can vary over the period of an engagement but theiraccumulative effect transports the driven object 42 relative tovibration element 26. It is believed that this transport is mostefficient if the direction of transport coincides with the direction ofmotion of the contact portion 44 at the point of the ellipse that isclosest to the driven object 42.

[0267] The speed of contacting portion 44 tangential to the ellipticalpath 100 is largest where the minor-axis of the ellipse intersects theelliptical path, and smallest where the major axis of the ellipseintersects the elliptical path. An ellipse whose major axis istangential to the engaging surface of driven object 42 is thereforeexpected to provide an efficient transportation mechanism. It can bebeneficial to use an ellipse whose major axis is inclined with respectto the engaging surface of driven object 42. In this situation, thecontact portion 44 moves towards the driven object 42 at a differentrate than the rate at which it moves away from it after having passedthe point closest to driven object 42. Inherent to the elliptical shape,a faster approach typically results in a slower retreat and vice versa,so that the process of engagement with the driven element 42 can beselected to be more gradual or more abrupt. At its extreme, such amotion is known as a saw-tooth motion. Motors that generate exactsaw-tooth motion are in the prior art. Purposefully employing aninclined ellipse in the present disclosure provides therefore some ofthe advantages only seen in those saw-tooth motors.

[0268] To ensure efficiency of transport, it is preferable that thefrictional engagement is sufficiently large, and that the contactingportion 44 moves against the direction of desired transport of drivenobject 42 only while the friction forces are reduced or vanish, whichoccurs when some or all of the contact portion 44 has lost contact withthe engaging surface of the driven object 42.

[0269] The amount of friction and wear depends also on the frictionparameters and the material combination used for the contact portion 44and the size of contact portion 44. These parameters also influence thestrength of the motor 20. More friction typically results in strongerforce but may also result in more wear. Material combinations that arebelieved suitable for use include steel, aluminum and glass on one sideof the contact, and glass, fiberglass, PMMA, PVC, ABS or steel on theother side of the contact. The friction parameters of glass surfaces aremodifiable chemically or physically by adding particles or etching atexture.

[0270] It is an advantage of the motor assembly 20 that the dimensionsof the engaging surface of the driven object 42 do not have to beprecise and that variations are accommodated by the resilient mountingsystem of the motor 20, which is discussed later. Also, it has beenshown that wear due to the vibrations can modify the contact portion 44of vibration element 26 and create a larger contact area. This effect isespecially strong at the beginning of the lifetime of the motor. Theeffect fades quickly, resulting in better motor performance. This wearcan be used to advantage since the resilient mount 50 urges the selectedcontacting portion 44 against the driven element 42, allowing forwear-in between harder and softer materials, that can reduce initialmanufacturing tolerances. As desired, the wear-in can also be used toincrease the selected contacting area 44.

[0271] Achieving desired elliptical motion: The size and orientation ofthe elliptical trajectory 100 depend on the amplitudes and phases usedto generate the ellipse. The ability to maintain a useful ellipticaltrajectory 100 of contact portion 44 over a sufficiently large frequencyrange depends on the vibration design properties of the motor assembly20.

[0272] It is known that a mode of the vibration element 26 undergoes asmooth phase change of −180 degrees with respect to the excitationsignal applied to the piezoelectric element 22 if the frequency ofexcitation is increased across the resonance frequency of the mode. Thewidth of the frequency range within which this transition occursincreases with the amount of mechanical damping in the system. It isdesirable that such a frequency range is sufficiently large in order toassure that the phase difference between two excited modes can remainsufficiently different from 0 or 180 degrees over an extended frequencyrange and can potentially sustain a desired elliptical motion of thecontact portion 44. This renders the motor 20 in principle lesssensitive to variations in manufacturing and operating conditions. Inorder to achieve a desired amount of damping at a particular location, aseparate dampening element could be added to any part of the vibrationelement 26 or the portion of the suspension that participates in themechanical vibrations. But preferably the damping that is inherent inthe system design and materials is used.

[0273] To achieve a stronger motor, it is also desirable if the excitedmodes of vibration show significant amplitudes at the contact portion 44near the desired frequency of excitation and thus it is preferable tohave a frequency of excitation that is close to a resonance frequency ofa selected mode. Since the amplitude of a mode at the contact portion 44also depends on the amplitude of its excitation, it is preferable thatthe vibration element 26 is designed to appropriately distribute themechanical vibrations generated by the piezoelectric element 22 to thevarious modes. This distribution can be achieved in a controlled fashionin a number of ways using combinations of damping, geometric andmaterial properties of the vibration element 26, and the forces that aregenerated between the vibration element 26 and the driven object 42 atthe contact portion 44. Conceptually, methods and modifications thataffect the force distribution are different from methods that affect theshape of a mode and its resonance frequency. In reality however, amodification that affects force distribution very often modifies also amode shape and its resonance frequency. For example, it is known for arod-like vibration element 26 that some modifications that woulddistribute mechanical energy forces to a pure longitudinal and a purebending mode would typically also couple the two modes together tocreate new modes of mixed type.

[0274] Distributing mechanical vibrations: Internal damping forces cancouple one mode to another so that the piezoelectric element 22 canpotentially drive a first mode, which in turn excites a second modeindirectly by way of damping. This effect is particularly strong if therespective resonance frequencies and the frequency of excitation lieclose together.

[0275] A first mode that is excited by the piezoelectric element 22 at acertain frequency can excite a second mode also by way of the contactforces generated in the contact portion 44. Specifically, the ellipticalmotion of the contact portion 44 can produce a force that is sinusoidalor a force that is intermittent with the same frequency that drives thefirst mode. This force then excites other modes in the vibration element26, as well as vibration modes of the driven object 42 discussedelsewhere. This form of excitation can be mutual, and this effect can bedeliberately used, so that formerly independent modes can be coupledtogether to form new modes. The orientation of the ellipse 100 at thecontact portion 44 and the portion of the ellipse during which contactforces are generated determine the phase with which a second mode isexcited relative to the first mode. This phase is preferably not amultiple of 180 degrees.

[0276] Which modes of vibration element 26 are excited by way ofcontact, and by how much they are excited, also depends on the positionand orientation relative to vibration element 26 of contact portion 44and engaging surface of driven object 42. The contact portion 44 can bechosen to lie in a plane of symmetry of the assembly 20, vibrationelement 26, resilient mounting system 50 or driven object 42, or not.Non-symmetric positioning can be used to excite modes that otherwisewould be harder to excite by the piezoelectric element 22 alone, forexample certain bending modes or torsion modes of vibration element 26.To the same end, the orientation of the engaging surface relative tovibration element 26 can be chosen to be perpendicular or parallel tocertain planes of symmetry, or not.

[0277] Location and orientation of piezoelectric element: Referring toFIG. 1, the vibrating element 26 preferably has an elongated, rod-likeshape with an opening 28 perpendicular to the longitudinal axis 25 ofthe rod. The opening 28 has dimensions slightly smaller thancorresponding dimensions of the piezoelectric element 22, so that thepiezoelectric element can be inserted into the opening 28 in a press-fitmanner. If the vibrating element 26 has a symmetric shape, and if thepiezoelectric element 22 is inserted symmetrical with respect to thelongitudinal axis 25, and if the contact between the piezoelectricelement 22 and the vibration element 26 is nearly perfect, then it isexpected that primarily only longitudinal vibrations in direction ofaxis 25 are generated. These vibrations can be transformed into bendingor other vibrations by way of the previously discussed contact forces atcontact portion 44, or they can be transformed by the action of theresilient mounting system 50 discussed below, which urges vibrationelement 26 against the driven object 42.

[0278] The piezoelectric element 22 can directly generate other thanlongitudinal vibrations in the vibration element 26 if element 22 isnon-symmetrically inserted into the opening 28, e.g., if thelongitudinal axis 95 of the piezoelectric element 22 is offset (cf. FIG.14) or inclined (cf. FIG. 15) with respect to the longitudinal axis 25of vibration element 26, or if at least one of the contact areas betweenthe piezoelectric element 22 and the resonator 24 is madenon-symmetrical. For example, the vibration element 76 in FIG. 5 has thelongitudinal axis of the piezoelectric element 22 offset from aprincipal longitudinal axis of the resonator 74. This offset couplesvarious modes of the resonator 74 and the vibration element 76.Moreover, the resonator 74 rotates about pin 78, and that may furthermodify vibrating modes of the vibrating element 76.

[0279] The more pronounced the modifications are that let thepiezoelectric element 22 be inserted in a asymmetric fashion, the morebending and other vibrations are typically excited. Also, suchmodifications typically couple formerly independent longitudinal andbending modes together to create new modes of mixed type. Torsion modesin a rod-like vibration element could also be excited.

[0280] In a preferred embodiment, the piezoelectric element 22 isinserted into the opening 28 in the resonator 24 such that the resonatorand the piezoelectric element 22 do not enter into perfect contact alongthe entire area where contact could be possible. To achieve such apurposefully partial contact during the insertion process, the sidewalls29 of the opening 28 could for example be deformed by the insertedpiezoelectric element 22 such that contact is lost in certain portionsof the potential contact area. Alternatively, partial contact can beachieved by making the potential contact surface of the piezoelectric 22non-even, for example by removing material in parts of the contact areaof the resonator 24 before inserting the piezoelectric into the opening28. In FIGS. 10 and 11, this could also be achieved by inserting a pin92 at a location offset from the depicted longitudinal axis 25. Also,inserts 94 (FIG. 16) could be used to provide localized contact areas atthe location of the insert. Moreover, combinations of the above methodsmay be used to achieve a desired partial contact and to induce a desiredcombination of lateral and longitudinal motion components at a desiredcontacting portion 44.

[0281] Shape of vibration element: The resonance frequencies of thevarious vibration modes typically decrease if the vibration element 26is made longer, and vice versa. Also, the shape and size of thecross-sections of the resonator 24 affect the resonance frequencies andmodes involving bending and torsion. For example, referring to FIG. 73,the cross-section of the resonator 24, or at least of a portion of thedistal end of the resonator 24 could be I-shaped, which can be used tovary the relative stiffness and resonance frequencies of modes involvinglongitudinal motion and lateral bending since the I beam cross-sectioncan have the stiffness along one lateral axis much different than thestiffness along the other lateral axis. It also produces a lower lateralbending stiffness without having to greatly increase the length of theresonator 24. FIG. 73 also shows a T-shaped cross section, which couldintroduce a twisting mode if the T was made non-symmetric about itsvertical axis. C-shaped cross-sections and variety of othercross-sectional shapes can be used to vary the resonance modes of theresonator 24 and of the vibrating element 26. Other non-symmetric,cross-sectional shapes can be used.

[0282] To purposefully achieve modes of vibration that can generate adesired elliptical motion 100 at the contact portion 44 of vibrationelement 26 so that the ellipse 100 is inclined with respect to thelongitudinal axis 25 of vibration element 26 and/or the engaging surfaceof driven object 42, it can be advantageous to have a non-symmetricdesign of the vibration element 26. For example, the resonator 24 couldbe made helical, or it could have an arched or an L-shape. Other shapesare possible. The asymmetric mass distribution that is achieved this wayresults in modes of vibration that are neither purely longitudinal norpurely transversal in nature, which is beneficial for generatinginclined elliptical motion 100.

[0283] Moreover, referring to FIG. 77 a further embodiment is shown thathas advantageous design features. This embodiment illustrates aresonator 24 that is not straight. Further, it illustrates the locationof the piezoelectric element 22 along an axis that does not intersectthe driven element. Moreover, it illustrates a different alignment andorientation of the piezoelectric element 22 and the resonator 24. Theaxes are inclined relative to each other, with the axis of piezoelectricelement 22 generally parallel with the axis 45 of the driven element 42.The axis 25 of the resonator 24 is inclined to bridge the gap betweenthe two axes 95, 45. The selected contacting surface 44 comprises acurved surface conforming the shape of the abutting contact area on therod-like driven element 42. The curved surface may be manufactured or itmay be generated by natural wear during operation of the motor. Theresilient mounting system accommodates motion of the selected contactsurface 44 that moves the rod 42.

[0284] Advantageously, the resilient mounting system comprises one ormore springs 50. In the illustrated embodiment, if the rod 42 is in ahorizontal plane, then a spring 50 a aligned in the horizontal planethrough piezoelectric axis 95 and perpendicular to (but offset from) thelongitudinal axis 45 provides the resilient mounting system.Advantageously, there are two springs 50 a extending on opposing sidesof the resonator 24 to provide a symmetric resilient mounting, althoughonly one spring 50 a could be used. The springs 50 a are shown connectedto the resonator 24 by interposing distal ends of the springs 50 abetween the piezoelectric element 22 and the opening 28 in resonator 24.Instead of separate springs 50 a, a single leaf spring element with itsmiddle abutting piezoelectric element 22 could be used.

[0285] Alternatively to spring 50 a, or in addition to spring 50 a, aspring 50 b connects to the resonator 24 adjacent the end 35 in an axisorthogonal to the horizontal plane. Depending on the relative stiffnessof the springs 50 a, 50 b, and the relative location of those springs,various motions of the driven element 42 can be achieved. Preferably,the motion is a combined rotation about, and translation along axis 45,but a pure rotation or a pure translation of the driven object 42 couldalso be achieved.

[0286] Suspension: A resilient mounting system 50, called thesuspension, is connected to the vibration element 26 to ensure that theselected contact portion 44 is consistently urged against the engagingportion of the driven element 42 so that the elliptic motion 100 of thecontact portion 44 can transport the driven element 42. Similarprinciples apply if the driven element 42 is resiliently suspended andurged against the contacting portion 44 instead. This consistentresilient force is preferably maintained even if the driven element hasa varying surface smoothness or configuration and if the contact portion44 shows signs of wear. For a small resilient force, these motors havebeen shown to transport the driven object 42 quickly, but provide smallforce. For a larger resilient force, the transportation speed decreases,but the transportation force increases. If the resilient force isselected too large, the driven object typically stops.

[0287] Depending on the location of the selected contacting portion 44and the configuration in which one or more vibratory elements 26 arearranged (e.g., FIGS. 23-42, different suspension systems will beneeded. A variety of suspension systems are illustrated in FIGS. 1, 2, 5and 17-22, and portions of the suspension system are discussed in thesection on Mounting Of Vibratory Elements & Driven Elements. Thesuspension system described here is primarily a spring-based suspensionsystem, but need not be so limited. The suspension could include leafsprings, coil springs and other types of springs; it could includeresilient materials such as elastomers or compressed gas springs, toname a few. The effect of the suspension system on the vibration modesof the vibratory element 26 will vary with the specific type ofsuspension system used and its arrangement.

[0288] For example, FIG. 74 shows a suspension system using a curved,flat spring 188 having a first end 188 a connected to base 52 and anopposing end 188 b connected to the vibratory element 26. In thedepicted embodiment, the spring 188 is interposed between one end of thepiezoelectric element 22 and the adjacent wall, which defines an opening28. The vibratory element 26 is inclined at an angle α relative to theengaging surface of the driven object 42. The curved spring 188 offersthe possibility of providing a smaller motor assembly 20 because thecurved spring can reduce the needed space for the suspension. The wheel46 could contacts the driven element 42 using a flat edge of the wheelconcentric with the rotational axis 65, as illustrated in FIG. 74. Thewheels 46 could also have contoured peripheries configured to engagemating shapes on adjacent portions of the driven element 42 in order toappropriately support and guide the driven element 42. Given the presentdisclosure, a variety of movable support configurations will be apparentto those skilled in the art.

[0289] Another example is shown in FIG. 1 where the vibrating element 26is mounted to and moves about the location where end 50 a is mounted tobase 52. The selected contact portion 44 is located relative to themounting of spring end 50 a to the base 52 so that a generally verticalaxis passes through both the mounting point 50 a and the contactingportion 44.

[0290] In contrast, the C-clamp configuration of FIG. 5 has thevibrating element 76 rotating about pin 78. A vertical axes passingthrough the contacting portion 44 is offset from a vertical axis passingthrough the pivot pin 78. The offset, combined with an asymmetriclocation of the piezoelectric element 22, results in a differentsuspension system that can have different characteristics.

[0291] Portions of the resilient suspension system typically participatein the vibrations of the vibration element 26 and therefore affect thevibration modes. The design of the suspension system is advantageouslysuch that it enhances the desired motion of the selected contact portion44.

[0292] If a resilient suspension system, such as spring 50 is connectedat a node of vibration at an operational frequency of the vibratorelement 26, then it does not participate in the vibration. But if theresilient suspension system is connected at a location other than a nodeof vibration at selected operating frequencies, then it creates anasymmetry that can couple various otherwise independent modes ofvibration of vibration element 26 together. This can result inelliptical motion 100 at the selected contacting portion 44 that isespecially useful if the engaging surface of the driven object 42 isinclined with respect to the vibration element 42.

[0293] For example, in the embodiment of FIG. 5, the vibration element76 oscillates about the pin 78, which can cause the contact portion 44to have an up-and-down motion along its elliptical path 100. Themounting of the vibrating element 46, 76 can result in a variety ofvibration modes of the motor assembly 20 and various movement of thecontacting portion 44.

[0294] Moreover, referring to FIG. 77 the further embodiment is shownthat is suitable for use in a torsional motion or rotational motion ofthe driven element. In this embodiment, the driven element 42 rotatesabout its longitudinal axis 45. The longitudinal axis 95 of thepiezoelectric element 22 is not aligned with the longitudinal axis 25 ofthe resonator 24. The axes are inclined relative to each other, with theaxis of piezoelectric element 22 generally parallel with the axis 45 ofthe driven element 42. The axis 25 of the resonator 24 is inclined tobridge the gap between the two axes 95, 45. The selected contactingsurface 44 comprises a curved surface conforming the shape of theabutting contact area on the rod-like driven element 42. The resilientmounting system accommodates motion of the selected contact surface 44that rotates the rod 42 about its longitudinal axis 45.

[0295] Advantageously, the resilient mounting system comprises one ormore springs 50. In the illustrated embodiment, if the rod 42 is in ahorizontal plane, then a spring 50 a aligned in the horizontal planethrough piezoelectric axis 22 and perpendicular to (but offset from) thelongitudinal axis 45 allows the rotational motion of rod 42.Advantageously, there are two springs 50 a extending on opposing sidesof the resonator 24 to provide a symmetric resilient mounting, althoughonly one spring 50 a could be used. The springs 50 a are shown connectedto the resonator 24 by interposing distal ends of the springs 50 abetween the piezoelectric element 22 and the opening 28 in resonator 24.Instead of separate springs 50 a, a single leaf spring element with itsmiddle abutting piezoelectric element 22 could be used.

[0296] Advantageously, but optionally, a spring 50 b connects to theresonator 24 adjacent the end 35 in an axis orthogonal to the horizontalplane. Depending on the relative stiffness of the springs 50 a, 50 b,and the relative location of those springs, various motions of thedriven element 42 can be achieved. Preferably, the motion ispredominantly or purely rotation about longitudinal axis 45, although acombined rotation about, and translation along axis 45 could also beachieved.

[0297]FIG. 77 also illustrates that the vibration element 26 andresonator 24 can be non-symmetric It also shows that the spring 50 canhave various locations, configurations and orientations. Indeed, thespring 50 can be a bending or torsion spring, each of which can affectthe suspension and resonant vibration modes of the system or of thevibratory element 26. FIG. 77 also shows that the spring 50 need not beconnected to the piezoelectric element 22. Moreover, the axis 25 of thepredominant vibrating portion of resonator 24 need not be parallel tothe axis 95 through the piezoelectric. Further, the contacting portion44 can be molded to conform to the abutting surface of the drivenelement. The molding can be preformed in the resonator 24, cut orotherwise formed into the resonator 24, or it can be formed by wear andrun-in.

[0298] A Mode of Operation to Reduce Friction:

[0299] It is an additional feature of the motors of this disclosure thatwhen excited at certain frequencies, which are not the operationalfrequencies, they produce a varying contact force at the contact portion44, and possibly liftoff, which can reduce the effective frictionalholding force on the driven object 44. In other words, it is easier topull the driven object through the motor when operated at thosefrequencies, then when the motor is turned off. This property ofselectively reduced friction can be beneficial in certain applications.

[0300] Theoretical Design Aspects

[0301] The piezoelectric 22 and resonator 26 are configured to achieve adesired motion of the selected contact portion 44 that moves the drivenelement 42. The contact portion 44 preferably moves in an ellipticalpath 100 as shown in FIG. 1. Changes in phase and amplitudes of tworectangular components of motion of the resonator 26 and theirsuperposition to achieve that elliptical motion are described here(similar results can be derived for oblique angles). By modifying thephase and amplitudes several properties of the ellipse useful to thepresent application in motor assembly 20 are better understood. Theseproperties include the orientation and lengths of the short and longsemi-axes of the ellipse that is the path preferably traveled by theselected contact portion 44. Other relevant properties could alsoinclude the speed by which the ellipse is traversed, which correlates tothe speed of the contact portion 44 and thus the speed with which thedriven element 42 moves. The design may require the direction of thesemi-axis of the ellipse to be aligned with certain dimensionaltolerances within the piezoelectric motor assembly 20. The design mayalso require that the lengths of the semi-axes of the ellipse 100 do notexceed certain predefined limits. Moreover, the ratio of the semi-axesof the ellipse 100 can be advantageously selected to provide greatermotion, or faster movement, with the ratio of the axes advantageouslybeing 5:1, preferably 10:1, and ideally from about 10-50:1.

[0302] Referring to FIG. 43, the ellipse 100 represents the potentialmotion of contact portion 44 of the vibrating element 26 as shown inFIGS. 1 and 5, among others. The ellipse 100 is generated by twocomponents of motion, the first acting in the E_(x)-direction (whichcorresponds to motion along the longitudinal axis 45 of the drivenelement 42 in FIG. 1). The second component of motion acts in theE_(y)-direction, which is perpendicular to the E_(x)-direction. The twocomponents of motion E_(x), E_(y) are generated at the selected contactportion 44 of the motor assembly 20. The mechanism used to generate thecomponents of motion do not affect the following disclosure. Localizedmajor and minor axes e_(x), e_(y), respectively, of the ellipse 100 arealso shown.

[0303] For illustration, the first and second components of motionE_(x), E_(y) are assumed to be sinusoidal with amplitudes A and B,respectively, and to have a phase difference of φ=π/2+Δφ [rad]. Butother waveforms could be used. The position vector r of the selectedcontact portion 44 located at the edge of the resonator 24 as depictedin FIG. 1, as a function of time, is:

r=A cos(ωt+φ)E _(x) +B sin(ωt)E _(y).

[0304] In this equation, ω is the frequency of the oscillation. FIG. 44shows an example of the partial components of motion for A=1, B=0.5, ω=1and φ=π/6 [rad]. The ellipse 100 of FIG. 43 is traversedcounterclockwise for |Δφ|<90°, and clockwise for 90°<|Δφ|<270°.

[0305] The lengths 2 a and 2 b of the long and short semi-axes are thencomputed from, respectively:

2a ² =A ² +B ² +{square root}{square root over (A⁴+B⁴−2A²B² cos(2Δφ))},

2b ² =A ² +B ² −{square root}{square root over (A⁴+B⁴−2A²B² cos(2Δφ))}.

[0306]FIG. 45 depicts how b/B depends on Δφ and the ratio B/A. FIG. 46depicts the dependence of a/A. It is important to notice that thedependence of b/B does not change substantially for ratios of B/A<=0.3.A good approximation of this dependence for |Δφ|<50° and B/A<=0.3 isgiven by the function$\frac{b}{B} = {1 - {\frac{\left( {{\Delta\phi}\lbrack{rad}\rbrack} \right)^{2}}{2}.}}$

[0307] The orientation angle α (FIG. 43) cannot exceed the valueatan(B/A) (see FIG. 47). As design rule, one has, for B/A<0.5${a\quad {\tan \left( \frac{B}{A} \right)}} \approx {\frac{B}{A}.}$

[0308] The angle α can for sufficiently small ratios B/A be approximatedby (see FIG. 48):${\tan (\alpha)} = {{- \frac{B}{A}}{{\sin ({\Delta\phi})}.}}$

[0309] The following example illustrates the usage of the previousmaterial. Assuming that B/A=0.3. From FIG. 47 we find that atan(B/A)≅15°. It follows then from FIG. 48 that for Δφ=45°,α≅0.8*15°=12°. FIGS. 45-46 indicate that b/B≅0.7 and a/A≅1.025.

[0310] This information illustrates how to change A, B and Δφ togetherin a way that preserves or achieves various properties of the ellipse100. In the previous example, the changes can be made such that theangle of inclination α (FIG. 1) between the longitudinal axis 25 of thevibratory element 26 remains close to 12 degrees in order to achieve alarge translation of the driven element 42. The changes may also be madeto ensure that 2 b, the length of the minor axis of the ellipse 100(FIGS. 1, 43) remains larger than a given value in order to ensure thevibratory element 26 causes the selected contact portion 44 to disengagefrom the driven element 42 sufficiently to not only avoid undesiredmovement of the driven element 42, but to avoid unacceptable wear of thedriven element 42. Over a relatively wide parameter range a desiredellipse 100 can be achieved that is particularly useful for moving adriven element 42 in the present invention. In the example above, thedriven element 42 would be preferably oriented in an angle of 12 degreesto the E_(x)-direction. But it should apparent to one skilled in the artthat the optimal angle is in general not restricted to this value.

[0311] Referring to FIGS. 1, 43 and 49-51, it is also advantageous toconsider the influences of a coordinate transformation from thecoordinate system having an axis aligned with the longitudinal axis 25of the vibratory element 26, to the coordinate system corresponding tothe elliptical motion of the selected driving portion 44. This canillustrate useful affects on the frequency response curves and thereforeon the performance and design of the motor assembly 20. FIG. 43illustrates the motor coordinate system defined by axes E_(x), andE_(y), where the E_(x) axis corresponds to the longitudinal axis 45 ofthe driven element 42 (FIG. 1). The ellipse 100 is believed to begenerated by a first and a second motion component of the selecteddriving portion 44 on the vibratory element 26 of FIG. 1. The localizedaxes of the ellipse 100 are represented by axes e_(x) and e_(y).

[0312] For example, we assume the first component of motion lies in theE_(x)-direction and has a transfer function that in the vicinity of aselected frequency can be approximated by a constant amplificationfactor g₁(s)=A. The second component of motion lies in theE_(y)-direction and has a transfer function that in the vicinity of aselected frequency can be approximated by a second order resonator givenby its Laplace transform:${g_{2}(s)} = {\frac{k}{s^{2} + {2\quad \omega_{0}s} + \omega_{0}^{2}}.}$

[0313] Here ω₀ is the (undamped) resonance frequency, and e is adimensionless damping parameter arising inherently from damping in themechanical system, i.e., the motor assembly 20 in this case.

[0314] The superposition of g₁(s) and g₂(s) yields transfer functionsG₁(s) and G₂(s) in the e_(x) and e_(y) directions, respectively. Forillustration, examples are given in which A=1 and ω₀=1. FIGS. 49-51depict G₁(s) and G₂(s) for k=0.01 and α=25 degrees. The parameter eincreases from FIG. 49 to FIG. 50 to FIG. 51. The combination of thesetwo signals results in a behavior where the phase difference Δφ betweenG₁(s) and G₂(s) undergoes an intermittent change that becomes morerounded as the damping in the system increases. This effect results inan expanded frequency range where the relative phase difference liesbetween 0 and 180 degrees, which makes it easier for a resonantfrequency to be found that results in a useful, elliptically shapedmotion. This frequency range is considerably wider than what would beachieve with the transfer function of a simple second order oscillator.Such a particularly widespread phase range can be used in conjunctionwith other design aspects to help select the shape and orientation ofthe resulting ellipse 100 as the selected driving frequency is changed.

[0315] The influence of the above coordinate transformation becomes moreinvolved as G₁(s) and G₂(s) are replaced by higher order, and morerealistic, transfer functions as they arise from the piezoelectric motorassembly 20. Such transfer functions can create relative phase shifts Δφbetween G₁(s) and G₂(s) that fluctuate between 0 and 180 degrees in evenwider frequency ranges, thus rendering the motor assembly 20 even lessdependent on production tolerances, material properties, temperaturevariations, and other manufacturing factors and criteria.

[0316] This phase shift between the longitudinal and lateral motion isused to achieve the desired elliptical motion. Phase shifts of between 3and 177 degrees are believed well suitable to achieve useful motion atthe selected contacting portion 44. A 90 degree phase shift results in acircular motion if amplitudes are equal. Preferably, but optionally, thephase shift results in non-circular motion of the selected contactingportion 44 in order to obtain greater movement along the major axis ofthe elliptical motion.

[0317] The portion of the ellipse 100 below the E_(x) axis can bethought of as reflecting the engagement of the driving portion 44 withthe driven element 42. By altering the shape of the ellipse 100 (i.e., 2a, 2 b measured along e_(x), and e_(y)) the duration of the engagementcan be varied and to some extent the pressure of that engagement can bevaried. Further, by altering the orientation of the ellipse 100 (i.e.,the angle of inclination α between the axis 45 of the driven element andthe major axis of the ellipse) the duration of the engagement can bevaried. As the angle of inclination α comes closer to aligning the e_(x)axis with the E_(x) axis, the duration of the contact between thedriving portion 44 and driven element 42 increases.

[0318] For practical reasons, the longitudinal axis of the drivenelement 42 may often be placed between the two axes E_(x) and e_(x). Butthe more important aspect is that these equations show that as theexcitation frequency of the piezoelectric 22 changes, the amplitude andphase of the selected driving portion 44 (i.e., ellipse 100) change.This shows the ability to alter the amplitude and orientation of theellipse 100 and thus alter the characteristics of the motion driving thedriven element 42. Moreover, the equations reflect an ability to offerthese variations over a wide range of amplitudes and frequencies whichoffers a flexibility in functional design characteristics of thepiezoelectric 22 not previously available. Further, the equationsreflect the ability to vary the engagement criteria to a sufficientextent that the manufacturing tolerances can be less, and potentiallysignificantly less than with many of the existing motors usingpiezoelectric drives.

[0319] Historically, these various manufacturing criteria have been soprecise that they result in costly manufacturing of piezoelectricvibratory elements 26, and the motors have narrow operating ranges andcriteria. Thus, the ability to use more liberal criteria offers thepossibility of significant cost savings in producing the motors whileoffering wider operating parameters.

[0320] The direction of the motion of the driven element 42 depends onthe relative orientation of the driven element 42 and the direction ofthe selection contacting portion 44 as it moves around its ellipticalpath of travel 100. Different points of the vibration element 26 canshow different vibration shapes. Typically areas with clockwise andcounterclockwise motion around elliptical paths 100, alternate along thelength of the vibration element 26. The driving direction of a rodshaped vibration element 26 can typically be reversed by turning thevibration element by 180 degrees about longitudinal axis 25.

[0321] The shape of the motion of the contact point 44 is important tothis invention. This shape must achieve more driving force in onedirection than in the other. This is typically achieved by increasingthe contact pressure while the selected contact portion 44 moves in thedirection the driven element 42 gets moved. When the contact portion 44moves in the opposite direction the contact pressure is reduced or thecontacting portion 44 even looses contact with the driven element 42.One important aspect is how to generate the appropriate motion.

[0322] Because of mechanical noise and unwanted vibrations, the shape ofthe ellipse does not always follow the ideal theoretical path. This mayresult in the selected contacting portion 44 sometimes performingmotions that are undesired, such as figure-eight shaped motion. Butthese motions may nonetheless regularly appear with the vibrator element26. They are, however, not used to drive the driven elements 42. This isclarified in the discussion of the three-dimensional vibration shapes ofthe contacting portion 44.

[0323] In the description only the two-dimensional shape of thevibration will be addressed. In actuality the contacting portion 44 willhave some slight motion in the third dimension, the directionperpendicular to both directions of the driving force along axis 25 andthe direction of the contact force between vibration element 26 anddriven element 42 which is generally along axis 45. These vibrationsmight also contain higher frequency components. As a result the motionof the contact portion 44 could look like a figure-eight motion ifprojected into certain planes. Although this figure-eight motion can beobserved, it is not relevant for the operation of the vibratory element26 driving the driven element 42 and is merely a side effect of unusedmotion.

[0324] Ideally, the major axis of the elliptical motion 100 is perfectlyaligned with the direction in which the driven element 42 moves in orderto optimize performance. Perfect alignment is difficult to achieve formany reasons, including manufacturing tolerances and performancevariations. Further, even the elliptical path 100 is not perfectlyelliptical and may vary over time. Variations in voltage, current, powerdisruptions or fluctuations, degradation over time, electrical noise,mechanical noise, electromagnetic interference, to name a few, canaffect the shape and smoothness of the elliptical paths 100. Thus, it isdesirable to be able to configure a system that can accommodate apractical range of variations in order to reduce manufacturing costs andassembly costs, and to produce a system that can accommodateenvironmental variations and other variations that arise during use ofthe system. Because of such variations, an alignment of about 0-5degrees will be considered to be aligned, in part because in mostinstances this variation from perfect alignment does not substantiallyaffect the performance of the systems disclosed herein.

[0325] The vibrator element 26 does not rely on traveling waves for themovement of the selected contacting portion 44. But any mechanical waveexisting in material also travels through it. In the present inventionsuch waves get reflected at some part of the vibration element 26causing another traveling wave that superimposes with the first one.This results in a standing wave, and in some instances this standingwave can be used in connection with a selected contacting portion 44.Several prior art motors require a wave that is not standing, but rathertraveling—with the driven object moving with or being moved by thetraveling wave. The traveling wave is different from the standing wave.

[0326] Practical Design Aspects:

[0327] The contacting portion 44 is the point of the vibrating element26 that comes in contact with the driven object 42 in order to move thedriven object. That contacting portion is typically a portion of theresonator 26, and is preferably on the distal end 36 of the resonator.The power of the motor assembly 20 to move heavier driven elements 42and the efficiency of the motor assembly 20 are functions of theperiodic motion of the contacting portion 44 and of the force betweenthe contacting portion 44 and the driven element 42.

[0328] The spatial motion of the selected contacting portion 44 is theresult of the superposition of several vibration modes of the motor.These modes are all excited, to varying amplitudes and relative phases,at the same frequency generated by the piezoelectric element 22. Theircontributions to the desired motion of contacting portion 44 and forcesapplied by contacting portion 44 are a function of the relativemagnitudes and the relative phase angles of each of these severalvibration modes. These vibration modes in turn are functions of themotor geometry, constitutive relations, and the material properties.

[0329] In order to increase the performance of the motor assembly 20,the following guidelines may be used. Preferably all of the followingguidelines are simultaneously satisfied at the selected contact portion44 in order to optimize the performance of the motor assembly 20, butcompromises of one or more of these guidelines can occur if theresulting motor performs satisfactorily.

[0330] The motion of the selected contacting portion 44 is ellipticalwith major and minor axes of lengths a and b, respectively. As usedhere, and unless specified otherwise, the reference to elliptical motionor to an ellipse includes ellipses with the major and minor axes areequal, which forms a circle. The reference to elliptical motion or to anellipse also includes ellipses in which either of the major or minoraxes are small relative to the other axis, which results in a veryelongated ellipse approaching a straight line.

[0331] The major axis of the ellipse is preferably aligned with thedriving direction of the driven element 42. The length of the major andminor axes, a and b, are both large enough to achieve their desireduses, and preferably large enough to provide optimum performance for theselected application. The generally preferred elliptical shape has anelongated major axis “a” relative to the minor axis “b” in order toincrease speed, and has a minor axis “a” sufficient to disengage thecontacting portion 44 from the driven member 42 during the returnportion of the ellipse, as discussed next. As discussed above, ratios ofabout 3:1 up to 150:1 or even greater are believed usable, although thehigher ratio's provide more linear motion and result in more impactmotion with the driven element.

[0332] The force at the selected contact portion 44 normal to thecontact surface on driven element 42 is large when the contactingportion 44 moves in the driving direction, and small (or zero), when thecontact portion 44 moves against it. If the force is zero, thecontacting portion 44 has lost contact with the driven object 42. Inthat lost-contact case, the backward motion of the vibratory element 26tip is very efficient, but the motor assembly 20 also loses tractionduring that period of time. This loss of traction should be consideredwhen evaluating motor efficiency and strength. If the normal force istoo large when the contact portion 44 moves against the drivingdirection, the driven element may not be properly transported in thedriving direction, which results in a loss of performance.

[0333] Moreover, the normal contact force between the selectedcontacting portion 44 and the driven element 42 is a measure of thefriction force between the contacting portion 44 and the driven object42. Larger normal forces provide the motor assembly 20 with strongerthrust. But the wear occurring over the repeated contact from the manythousands of cycles of elliptical travel must also be considered. Largercontact areas on the contacting portion 44 have the advantage oftolerating more defects in the surface of the driven element 42 thatengages the contacting portion 44.

[0334] In the embodiments thus far disclosed, the selected contactingportion 44 is often illustrated as being located on one edge of thedistal end 36 of the vibration element 26, in part because the desiredelliptical motion can be readily achieved at that location. Moreover,the edge location provides a narrow area of contact and good frictionalengagement. But it is not necessary that the selected contacting portionhas to be located on an edge. Moreover, typically some material wearwill wear out the edge and provide a flat or flattened contact surface44 after some period of use. This wear typically does not affect theoperation or use of the motor assembly 20. As discussed elsewhere, thecontact portion 44 can also be located at other places on the vibrationelement 26. For example, the contact portion 44 could be located on theside of the vibration element 26 as in FIG. 62. The selected contactingportion 44 does not have to be a point contact. The particularapplications will thus influence the size and location of the selectedcontacting portions 44.

[0335] The displacement of the contacting portion 44 in the drivingdirection and the normal contact force are not in phase. These twoquantities form an ellipse when plotted in a displacement/force diagram.The orientation of the major axis of this ellipse with respect to thedisplacement axis provides another design parameter. Depending on thisorientation, the maximal contact force is generated earlier or laterduring the forward motion of the tip. In a certain sense this could beinterpreted as somewhat analogous to a saw-tooth-like movement. Becauseuseful motion can be achieved when one semi-elliptical axis of theelliptical path 100 is about 5, 10 or more times greater than each otheraxis, even relatively small motions can be of potential use for one ofthe semi-axes.

[0336] The motion of the selected contacting portion 44 is the result ofthe vibrations of the entire motor assembly 20 and its components. Largemotions of the selected contacting portion 44 are achieved if theexcitation frequency lies close to a resonance frequency of the system,and if the selected contacting portion 44 is located where a largeamplitude occurs. In order for the motion of the selected contactingportion 44 to be multi-directionally large, the motor assembly 20 isadvantageously designed to have several resonance vibrations clusteredin a selected frequency range. For example, if the natural frequency ofa bending mode is close to that of a longitudinal mode, and theexcitation frequency lies in between the frequencies that excite thesebending and longitudinal modes, then the resulting motion of theselected contacting portion 44 will have moderately large amplitudes.The elliptical nature of the motion of the selected contacting portion44 is generated by the phase difference of the respective motions. Thephase difference is generated in part by the damping in the system.Various combinations of these factors can be used to achieve the desiredmotion of contacting portion 44 and to achieve other criteria of themotor assembly 20, such as power, reliability, wear, etc.

[0337] The absolute and relative locations of the resonance frequenciesand vibration modes of the motor assembly 20 are affected by a multitudeof parameters. The following factors can be used to configure anacceptable design of the motor assembly 20.

[0338] Lower vibration modes are generally stronger than highervibration modes because the lower vibration modes store relatively lesselastic energy, leaving more energy for driving the object 42 throughthe selected contacting portion 44.

[0339] The location of the longitudinal resonance of the vibratingelement 26 in a frequency diagram is affected mainly by the length ofthe piezoelectric 22 and resonator 24 and by the material properties ofthe parts. The first longitudinal mode is by far the strongest andtherefore the more desirable mode to use.

[0340] The location of the longitudinal resonance of the vibratoryelement 26 in a frequency diagram can further be affected by the motorsuspension, i.e., by the spring steel support 50 (FIG. 1) or othermechanisms that connect the vibratory element 26 to its housing. If anatural (resonance) frequency of the support such as spring 50 isbrought close to the longitudinal resonance frequency of the vibratoryelement 26, it has the effect of splitting the longitudinal frequencyinto two frequencies which are close to each other. The phases of themodes fluctuate strongly between 0 and 180 degrees in these resonanceareas. Resonance splitting can therefore be used to spread the workingregion of a motor over a wider frequency range, making the motortherefore more robust.

[0341] Phase differences other than 0 and 180 degrees are induced bydamping mechanisms. In order to expand this effect over wider frequencyareas, additional damping elements such as damping layers can be addedto the vibratory element 26, or to various portions of the motorassembly 20. Also, internal damping is affected by the materialproperties of the piezoelectric 22 and resonator 24 and by the way inwhich they are assembled. These factors in turn can be affected by thematerial's history, i.e., its manufacturing process.

[0342] Moreover, whether the damping is inherent in the system materialsor added by design components, the damping can be used so that a primaryresonance mode is used to excite a secondary vibrational mode thatresults in the desired elliptical motion of a selected contactingportion 44 along path 100. Recall that the elliptical semi-axes can haveamplitude ratios of 5, 10 or more, such that a vibration mode excited bydamping need only have an amplitude of 1/5, 1/10 or so of the amplituderesulting from the primary vibrational mode. Because damping can couplevibration modes, the damping can be used to achieve the desiredelliptical motion of the selected contacting portion.

[0343] Bending resonance vibration modes are affected mainly by thelength and cross-sectional areas and shapes of the piezoelectric 22 andresonator 24 and also by the material properties of those parts. Lowerresonance vibration modes are stronger than higher ones. Guidelines forplacing and splitting of resonance longitudinal vibration modes alsoapply to bending modes.

[0344] Shearing resonance vibration modes can contribute to thelongitudinal motion of the selected contacting portion 44, especially ifthe contacting portion 44 is located at a distal end 36 of the vibratoryelement 26 and on an edge of the distal end. The shape of thecross-sections of the resonator 24 affects these resonance vibrationmodes, as does the placement of the piezoelectric 22 relative to theresonator 24. Further, as an example, see FIG. 2. If the longitudinalaxis of the piezoelectric 22 is appropriately offset from thelongitudinal axis of the resonator 24, an edge of the distal end 36 canhave a shearing resonance that causes opposing edges at distal end 36 topivot about axis 40. Removing material close to the centerline of themotor can have an especially strong effect on this resonance mode. Oneconfiguration with material removed along the centerline is shown inFIG. 52, and described later.

[0345] Torsion resonance vibration modes can be used to supportselected, and preferably vertical motion of the selected contact portion44 if the portion 44 is close to a side of the vibratory element 26. Thetorsion resonant vibration modes are usually of smaller magnitude thanother vibration modes, but they offer the possibility of using variousportions along the length of the vibratory element 26 to drive variousobjects. Torsion resonant vibration modes could be used to rotate thedriven element 42 in the embodiments of FIGS. 23, 25, 27, 28, 29, 30, 32and others. Torsion resonant vibration modes could be used to translatethe driven element 42 in the embodiments of FIGS. 38-40.

[0346] Resonant vibration modes arising from cross-sectional contractionare of little benefit when the driven element is elongated, such as therod-like driven element 42 depicted in FIG. 1. The cross-sectionalcontractions appear at frequencies that are too high to produce readilyusable amplitudes. Cross-sectional contraction is governed by thePoisson-effect. This effect is strongest where the longitudinal strainsin the piezoelectric element 22 or resonator 24 motors are the highest,i.e., where the stresses are highest. Cross-sectional contraction cantherefore be large where the piezoelectric element 22 is connected tothe resonator or whatever frame is holding the piezoelectric element andthe portion of that connection in which the forces are high. Thiscontraction can drive the bending vibrations of the thin sidewalls 29(FIG. 1) of the resonator 24. If the bending resonant vibration modes ofthe sidewalls 29 are tuned to the longitudinal vibration mode of thevibratory element 26, yet another splitting of natural vibrationfrequencies can occur with similar benefits as mentioned above.

[0347] The piezoelectric element 22 generates predominantly longitudinalforces in the resonator 24 within which it is mounted. Coupling of theselongitudinal forces from the vibratory element 26 into directions otherthan along longitudinal axis 25 creates a number of other possiblevibration modes within the vibration element 26, such as bending, shearand torsion. The intensity of the coupling of the longitudinal motionwith other vibratory motions within the vibratory element 26 candetermine the relative amplitudes of the various modes of the vibratoryelement 26 and therefore their relative contributions to the motion ofthe selected contact portion 44. Coupling can be generated by materialproperties, geometric imperfections and asymmetries within thecomponents of the vibratory element 26, primarily the piezoelectric 22and the resonator 24.

[0348] Some of these coupling effects are often poorly defined,difficult to analyze, and hard to measure or design. Well-definedmechanisms are therefore preferable. These mechanisms include mountingthe piezoelectric element 22 off-center of the longitudinal axis 25, orat an angle to the longitudinal axis 25 of the vibratory element 26, orusing flexible mountings for the vibratory element 26 such as a spring50 or similar elements. In the case of a spring 50, the longitudinalmotion of the vibratory element 26 generates bending in the spring 50.The end 50 b of the spring that is clamped to the vibratory element 26is forced to bend or possibly to twist. This bending or twisting causesbending moments to be generated in the vibrational element 26. Theconfiguration of the spring 40 could be used to vary the vibrationalmode, as for example by introducing bends, edges and similarmodifications into a flat metal spring. Furthermore, the spring 50 canbe made more flexible at specified locations to better define an axis ofrotation about the flexible portion, if that is useful to the design.Coupling of vibration modes within the vibratory element 26 can also beachieved if the piezoelectric element 26 is selected or configured orexcited to perform other than pure longitudinal motions.

[0349] Several additional factors are preferably considered inconfiguring the vibratory element 26 and the motor 22. These factorsinclude: the orientation of ellipse 100 in which the selected contactportion 44 moves when it is not in contact with anything; theorientation of the force-displacement ellipse of the contact portion 44when it is in contact with the driven element 42; and an estimate ofmechanical power generated at the selected contact portion 44 when it isin contact with the driven element 42.

[0350] Reversing Direction

[0351] If a principle of operation of the vibration element 26 is knownto transport the driven object 42 in one direction at a first frequency,it is desirable to use the same principle of operation at a secondfrequency to transport the driven object in the opposite direction. Sucha design is not only useful for vibration elements that operate usingelliptical motion, but also for vibration elements that operate on otherprinciples. The vibration modes of the vibration element 26 that producethe transporting motion in the contacting portion 44 at the firstfrequency are not necessarily the same as those that produce thetransporting motion at the second frequency, nor are they necessarily ofthe same type.

[0352] It is an advantage of such a multi-directional designthat—provided the vibration element 26 is appropriately designed—thesame mechanical components that are necessary to achieve unidirectionalmovement can be used to achieve bi-directional movement at two distinctoperational frequencies. In particular, a single vibration source 20,e.g., a piezoelectric element, is sufficient.

[0353] The realization of a multi-directional design is simplified ifthe axis 25 of vibration element 26 is oblique to the direction oftransport of driven element 42. Also, in many cases the shape of themotion of the contacting portion 44 at either operational frequency maynot be optimal to achieve maximal force or speed of transport, but onlya compromise to achieve suitable bi-directional performance.Furthermore, the frequency range within which the vibration elementtransports in one direction is not necessarily as large as the rangewithin which it transports in the other. Testing has shown that afrequency range of 5 kHz at a first frequency and at least 300 Hz at thesecond frequency are possible to move or transport a driven element inopposing directions.

[0354] Illustrative Designs

[0355] Various modifications on the design of the resonator 24 holdingthe piezoelectric element 22 are possible to enhance the performance ofthe vibratory element 22. The following implementations are somepossibilities. Combinations of these following embodiments, and of theprior embodiments, are possible. All combinations of methods forclamping the piezoelectric element 22 and of the various mountingmethods are also believed possible.

[0356] FIGS. 52-55 show a vibratory element 26 having a resonator 24with a slot 112 extending from adjacent the cavity 28 to adjacent thedistal end 36, and extending through the resonator, along the directionof longitudinal axis 25. The slot 112 preferably has rounded ends andparallel sides. But the slot could have rectangular shaped ends. Thereare advantages to using longer, narrower 112 compared to wide slots asshown in FIG. 54. The narrower slots 112 result in beams 114 with largerdimensions, so that manufacturing tolerances have less effect on theresulting vibration. If the slots 112 are large, the walls 114 areusually smaller in dimension so that errors in manufacturing have alarger effect on the vibrational performance.

[0357] The slot 112 preferably opens onto the same surfaces of theresonator 24 as does the opening 28. But this need not be so, as theslot could open onto other surfaces of the resonator 24 depending on thevibrational modes and configurations that are desired. FIG. 55 shows theslot 112 opening onto a lateral surface turned 180 degrees from theorientation of the opening 28. Various angular orientations arepossible, especially if the resonator 24 has a cylindrical body shape.The slot 112 creates a resonator with two beam segments 114 a, 114 b, onopposing sides of the slot, each of which forms a portion of resonator24.

[0358] In FIGS. 52-54, the slot 112 is illustrated as fairlysymmetrically located in order to produce side-beams 114 ofapproximately equal dimension with close vibrational modes andfrequencies. But the slot 112 need not be symmetrically located asreflected in FIG. 55, and can be located to produce beams 114 a, 114 bof very different dimension and with different resonance frequencies.Moreover, more than one slot 112 can be used.

[0359] The slot 112 in the resonator 24 can thus create an increasednumber of beams 114 in the resonator, with each beam vibrating at itsown eigenfrequencies and selected for that very reason. The increasedeigenfrequencies leads to an increased number of phase shifts of thevibrations in the resonator 24. By having two almost identical beams 114a, 114 b with eigenfrequencies very close together, it is also possibleto get a wider frequency range with high amplitudes.

[0360] The slot 112 also changes the mass distribution of the resonator,the bending of the resonator, and the shear stiffness of the resonator24. Each of these changes has an influence on the resonant frequenciesand resonant vibration modes of the resonator 24 and of the vibratoryelement 26. This gives a flexibility of design that allows a broaderrange of frequencies to excite the requisite vibration modes ofvibratory element 26 while allowing lower manufacturing tolerances.

[0361] In FIG. 53, the opening 28 for the piezoelectric element 22 hasrounded ends rather than flat ends over the portion that abuts thepiezoelectric element 22. The contact area between piezoelectric element22 and the end of the opening 28 comprises two lines when thepiezoelectric element has a square or rectangular cross-sectional area.This can provide a more defined contact. If the opening 28 is formed bya wall abutting the piezoelectric element 22, the wall is typically notperfectly flat and not perfectly orthogonal to the longitudinal axis 25.Moreover, the end of the piezoelectric element 22 is not perfectly flatand not perfectly orthogonal to the centerline (e.g., longitudinal axis25). Thus, when the end of the piezoelectric element 22 abuts the walls(e.g., end walls 31) defining the opening 28, it is possible that thepiezoelectric will not be compressed along its centerline, with theresult that the piezoelectric will be compressed along an offset axis ora skewed axis. The offset axis or skew axis can result in a variation ofvibrational modes. Alternative ways of resolving this contact locationare discussed relative to FIGS. 9-16.

[0362]FIG. 56 shows an embodiment with two slots, on each side of theopening 28, along the piezoelectric element 122. The slots 112 open intothe opening 28 to form an “H” shaped configuration with thepiezoelectric element 122 mounted at the center of the “H”. Thisconfiguration makes it easier to press-fit the piezoelectric element 122into the resonator 24 since the sidewalls 29 can take more deformationbefore necking begins.

[0363]FIG. 57 shows an embodiment in which the opening 28 is formed inone leg 114 defined by centrally located slot 112, resulting in the leg114 a being divided for a portion of its length into further legs 114 c.Configurations such as this can have a high shear contribution to themotion at the selected contacting portion 44, which is illustrated asbeing aligned along the axis of leg 114 a. A different selectedcontacting portion 44 b on leg 114 b could be used to drive a differentelement at a frequency other than that used to activate the driving modeof leg 114 a. A third potential contacting portion 44 c on the leg 114could represent yet another frequency to yet another driven element whenactivated. This is another illustration that the selected contactingportion 44 need not always be at the same location on the vibratoryelement 26, as it will depend on a variety of factors, including thenumber, configuration and arrangement of the vibratory element(s) 26 andthe configuration of the driven element or elements motor assembly 20.

[0364]FIG. 58 shows an embodiment having a hole 116 in the resonator 24.The hole is shown extending along the longitudinal axis 25 of thevibratory element 26, but it could be located off-axis, or skewedrelative to that axis 25. The hole 116 is shown as opening onto thedistal end 36, but it could be formed on any of the surfaces of theresonator 26. The hole 116 is preferably cylindrical and results fromdrilling of the hole as close tolerances can be maintained at low costwith such holes. But other shapes could be used, as a drilled hole canbe broached to achieve various cross-sectional shapes. The diameter ofthe hole 116 can vary depending on the desired effect, as the holechanges the mass distribution by removing material, and it changes thestiffness of the material remaining after the hole is formed.

[0365]FIG. 59 shows an embodiment with a larger mass behind thepiezoelectric element 122, located between the piezoelectric element 122and the proximal end 35 of the resonator 24 that is opposite the distalend 36. This extra mass enhances the vibration of the distal end 36 ofthe vibratory element 26 and is useful when the selected contactingportion 44 is on the distal end 36.

[0366]FIG. 60 illustrates an embodiment with multiple sidewalls 29. Itis possible to not only have solid sidewalls 29 next to thepiezoelectric element 22, but it is also have a more complex sidewallconfigurations.

[0367]FIG. 61 shows a further embodiment in which the piezoelectric issubstantially enclosed and surrounded by the frame. This configurationis akin to inserting batteries into a flashlight. The opening 28comprises a close-ended hole, with the end 120 of the hole having eithera conical shape or a flat shape depending on the drill used to createthe hole. A cap 122 threadingly engages corresponding threads on the endof the hole 28 to compress the piezoelectric element 22 placed in thehole. The cap 122 is shown as having a curved end 124 to abut the cap 34on the abutting end of piezoelectric element 22 and create a pointcontact. Preferably, one or more small holes 126 are formed in thesidewalls 29 defining the opening 28 so that the electrical wires 30 canbe connected to the piezoelectric element 22. But other ways ofproviding electrical connections can be devised. The end 120 againstwhich the piezoelectric element 22 abuts forms an area contact if thebottom 120 is flat; it forms a four point contact if the cross-sectionof the piezoelectric or any protective cap 34 (not show) is square; andit forms a line contact if the cross sectional area of the piezoelectricor any protective cap 34 (not shown) is round.

[0368] Preferably the resonator 24 is machined or cast of non-ferrousmetal, preferably aluminum. The resonator could be sintered ofappropriate materials. Moreover, it is believed possible that theresonator could comprise two separate sections joined by an appropriateadhesive to opposing sides of the piezoelectric element 22. Further, theresonator 24 could be formed of a suitable ceramic material. If formedof a ceramic material that is sintered, the resonator could be sintereddirectly to the piezoelectric during the sintering of the resonator 24.

[0369] Suspension Of The Driven Element: The driven element 42 ispreferably suspended so that it can move relative to the vibratoryelement 26 and support or move a desired load. Usually the load is movedby pressing a portion of the driven element 42 against the load, as forexample a fiberglass rod connected to a CD tray that is movedreciprocally in and out of a housing by a linear motor assembly 20. Butin some situations the driven element 42 itself may be the desired load.The driven element 42 can be suspended on bearings. Less expensivemethods are to suspend the driven element on small wheels, or to usebushings as linear bearings. The bushings are believed to work well withrod-like driven elements 42. A low friction and stiction coefficientbetween the bushings and a glass or fiberglass rod reduces theperformance loss of the motor assembly 20 due to friction.Self-lubricating bearings are desirable to further reduce frictionlosses. Other methods are possible. Other driven objects like a wheel ora ball also easily be suspended on an axle.

[0370] When the driven element 42 comprises a rod, it can also besuspended on at least four balls such that the rod can move linearly.The stiction of such a mounting using four Delrin balls is believed tobe less than with four ball bearings. The balls preferably need to runin grooves in order to transfer radial loads applied to the balls by therod. Thus, the rod could be grooved to provide a driven element 42 withlongitudinal grooves in it when the configuration of the motor assembly20 is arranged to translate the rod. The orientation of the grooveswould change depending on the desired movement of the rod or drivenelement 42. Further, the length of the grooves could limit the motion ofthe rod.

[0371] A plate driven by the vibratory element 26 could also besuspended on at least three balls. This would give the motion of theplate three degrees of freedom. Other methods are possible.

[0372] The driven element 42 could be suspended in a manner thatresiliently urges it against the selected contacting portion 44, usingprinciples discussed above for mounting the vibratory element 26. Oneresilient support is discussed regarding FIG. 6 above.

[0373] Electronics

[0374] A number of different electronic circuits can be used to drivethe piezoelectric element 22 of vibratory element 26 since the motor 26is functional with a variety of different signal shapes applied to thepiezoelectric element 22, as long as the power spectrum of the inputsignal provides a substantial amount of vibratory energy at the desireddriving frequency sufficient to achieve the desired motion of theselected contacting portion 44. This ability is an advantage over thoseprior art motors that require specialized, more expensive electronics togenerate special waveforms, such as, for example, saw-tooth waveforms.Some specific examples of driver circuits are shown in FIGS. 63 to 66.

[0375]FIG. 63 shows an example of a driver circuit, preferably using ahalfbridge 152 such as a NDS8858H halfbridge available from FairchildSemiconductor. A discrete halfbridge is also believed suitable, but isnot as preferred for size reasons. A rectangular input timer-signal 150of specified frequency can be used to repeatedly switch between theinputs of the integrated halfbridge 152. This process generates anoscillatory waveform in the capacitor 154, which represents thepiezoelectric element 22. It is however not necessary for the signal 150to be rectangular as long as it reaches the necessary thresholds thatcan switch the halfbridge 152. The signal 150 can thus be generated by amicrocontroller, or by other suitable signal generators such as a LM555timer circuit available from National Semiconductor. The inputtimer-signal 150 is used to switch between the inputs of the halfbridge153. The period during which one of the said inputs is connected to theoutput of the halfbridge is determined by the input signal 150 and canbe appropriately chosen. Typically, the cycle during which the supplyvoltage (VCC) is connected through to the output of the halfbridgeaccounts for about 50% or less of the time in order to achieve the bestenergy efficiency in the circuit and in the piezoelectric element 22. Ifthe signal 150 is high, the n-channel transistor 153 a in the halfbridge152 becomes conductive and discharges the capacitor 154. After thisdischarge, it is preferable for the signal 150 to change to a lowerlevel so that the p-channel transistor 153 b in the halfbridge becomesconductive instead and charges the capacitor 154. This process can berepeated indefinitely and, since the capacitor 154 represents thepiezoelectric element 22, it results in a vibratory motion of thepiezoelectric element 22 and therefore of the vibratory element 26 (FIG.1).

[0376] As an alternative, one of the transistors 153 a, 153 b in thedriver circuit can be replaced with a component 156, e.g. a passivecomponent like a resistor, or an active component such as a constantcurrent diode. Such an alternative embodiment is shown in FIG. 64, wherethe transistor 153 b has been replaced with a component 156 such as aresistor.

[0377] In accordance with specific embodiments, the driver circuits ofFIGS. 63, 64 have the advantage that they can be implemented within anintegrated circuit, e.g. as part of a microcontroller.

[0378]FIG. 65 shows an alternative driver circuit for the piezoelectricelement 22 that uses a switched resonance circuit having a capacitor 154(piezoelectric element 22), an electromagnetic storage device, such asinductive coil 158, and optional resistor 156 connected in parallel. Oneadvantage of using a resonance circuit to drive the piezoelectricelement 22 is the ability to lower the supply voltage (VCC) to batterylevel (e.g. 3V) while maintaining the higher voltages necessary tooperate the piezoelectric element 22. Moreover, the entire circuitconsists of only three electronic parts besides the capacitor 154, whichrepresents the piezoelectric element 22.

[0379] In FIG. 65, an input signal 150 (like the one previouslydescribed in the halfbridge driver circuit of FIG. 63) is used to switcha control element 153, such as transistor, on and off in awell-determined fashion. Typically the cycle during which the transistor153 is conductive is chosen to be about 50% or less in order to achievethe best energy efficiency in the piezoelectric element 22. When theinput signal 150 is high, the transistor 153 becomes conductive andreverses the charge of the capacitor 154 while increasing the currentthrough the coil 158. The current in the coil 158 reaches its maximumwhen the capacitor 154 is fully charged. At that point in time, the coil158 stores a maximal amount of energy in its electromagnetic field, andit is preferable if the input signal 150 is set to low so that thetransistor 153 is no longer conductive. The energy stored in the coil158 sustains the flow of current, which in turn reverses the charge ofthe capacitor 154 resulting in an increased voltage across the capacitor154 and therefore the piezoelectric element 22.

[0380] When the capacitor 154 has fully reversed its charge and if thecircuit adjustments are correct the energy in the coil 158 increases thevoltage across the capacitor 154 beyond the supply voltage (VCC). Whenthe coil 158 has relinquished its energy, the voltage across thecapacitor 154 reaches a maximum, and the capacitor 154 now stores theentire electric energy of the system. Next, the current flow through thecoil 158 reverses which in turn causes another reversal of the capacitorcharge. At this point or shortly thereafter, it is preferable if theinput signal 150 is switched to high again so that the cycle can berepeated.

[0381] The resistor 156 is not necessary for the operation of thecircuit of FIG. 65, but it provides a method to shape the waveform atthe capacitor 154 and to cut off possible voltage peaks that canoriginate from the fast switching of the current through the transistor153, hence reducing potential electromagnetic interference as well asleakage of vibratory energy into undesired frequency spectra.Alternatively, the resistor can also be put in series with the inductor158. As a further alternative, it can be beneficial to place theinductive coil 158 in series with the capacitor 154 to form another typeof electric resonance circuit. If the resonance frequency of thiscircuit is chosen sufficiently close to an operation frequency of themotor, higher voltages at the piezoelectric element 22 can be achievedwhile maintaining relatively low electric power consumption. Asmentioned earlier, the inductor 158 can advantageously also be a wirecoil made from the same wire that connects the capacitor 154.

[0382] Further, referring to FIGS. 78-80, it is possible to integratethe coil 158, and even the resistor 156, directly into the vibratoryelement 26 by, for example, wrapping an insulated wire around thevibratory element 26 to form an inductive coil as shown in FIG. 78. Insuch an embodiment, the two ends of the wire coil 158 can concurrentlybe used as electrical leads to the piezoelectric element, as shown inFIG. 79. The wire coil 158 can be wound around the resonator 24 as inFIG. 30, or separate as in FIG. 80. These configuration place inductivecoil 158 in parallel to the capacitor 154 and save additional wiring,although the coil 185 could be placed in series, with or without thedamping resistors, half-bridge or single transistors.

[0383] Moreover, the inductive coil 158 can be mounted close to thepiezoelectric element 22 with which it can form the electric resonatorcircuit. The physical proximity of the piezoelectric element 22 and coil158 can reduce the inherent electrical resistance in the electricalconnections of those parts and can make the circuit more effective,especially since most of the current used to drive the motor oscillatesin this electric resonator. As a result, the wires leading from theelectric resonator consisting of the coil 158 and piezoelectric element22 to the signal generating unit can be reduced in diameter andincreased in length and may result in lower electrical interference.

[0384] A source of electrical signals, such as a signal generator, iselectrically connected to the vibratory element 26, and the source ofvibratory motion, 22, through various ways, e.g., a pair of wires 30. Inorder to move the driven object 42 in a first direction, the signalgenerator produces an electrical signal with a spectrum whose dominantfrequency is the corresponding operating frequency. Typical and usablesignals include, but are not restricted to, pure sinusoidal, triangularand rectangular waveforms. Similarly, a signal with a spectrum whosedominant frequency is a second or third operating frequency, can causethe driven object 42 to move in a second or third direction.

[0385] The capability of the various vibratory motors described hereinto reliably operate with a variety of waveforms is an advantage overthose prior art motors that require special waveforms other thansinusoidal waves to function, e.g., saw-tooth waveforms, and that wouldnot function reliably with a purely sinusoidal waveform. Therefore,since the quality of the signal applied to the piezoelectric element 22can be less than compared to some prior art motors, the signal generatorcan have a simpler construction, which results in a reduced cost of theentire motor system.

[0386] Furthermore, it is desirable to have all electrical signalsproduced by the signal generator communicated through the same set ofelectrical connections to the vibratory element 26, and particularly tothe piezoelectric element 22, e.g., by wires 30. When all signals arecommunicated through the same electrical connections, there is no needfor a unit that switches between various selected connections. Thisfurther simplifies the vibratory motor compared to prior art motors.Further, some prior art devices generate a phase shift between twoelectrical signals and then communicate the signals individually throughseparate electric connectors to at least one piezoelectric element, andthe present, more simplified electrical connection can avoid that morecomplex design. This can further reduce the cost of the motor incomparison to some prior art motors.

[0387] As illustrated in FIGS. 78-80, the piezoelectric element 22 canbe sized to extend beyond the portions that engage the walls forming theopening 28. Thus, the piezoelectric element 22 is shown as extendingbeyond the end walls 31. This variation in the dimensions of thepiezoelectric element can be used to vary the value of capacitor 154,and thus the performance of the control circuits, such as the circuitdepicted in FIG. 65.

[0388] One potential disadvantage of the driver circuit of FIGS. 65 and78-80 is due to negative voltages that can appear across the capacitor154. Negative voltages can be damaging to the piezoelectric element 22,which is a polarized electrical component. In order to amend thesituation for piezoelectric elements susceptible to negative voltages, amodification of the circuit can be provided as discussed relative toFIG. 66.

[0389]FIG. 66 shows a driver circuit suitable for use with apiezoelectric element 22 that may be more sensitive to a negativevoltage. In this circuit, a second physical capacitor 154 b is added tothe piezoelectric element 22 (represented as capacitor 154 a), ormultilayer piezoelectric element 22, if it has multiple piezoelectriclayers that are electrically split as shown, can be represented as twocapacitors 154 a and 154 b. Also, another resistor 156 b is included inthe circuit in addition to the existing resistor 156 a. Parallel to theresistors 156 and the capacitors 154, two diodes 160 a, 160 b are added.

[0390] The orientation of the diode 156 a prevents the voltage of thenode between the two resistors 156 a, 156 b from falling below thesupply voltage (VCC). The voltage across the capacitor 154 a thereforecannot become more negative than the typical voltage drop across aconductive diode (about 0.5-0.7 Volts). This small negative voltage canbe sustained by most piezoelectric elements.

[0391] If, in the same manner as before, the circuit is excited by theinput signal 150 to resonate, the amplitude of the oscillating voltageacross the piezoelectric element 22 (represented by capacitor 154 a) canbe made larger than the supply voltage (VCC), but the voltage cannotbecome negative. A similar statement holds true for the physicalcapacitor 154 b so that a polar electrical component may be chosen thereas well. Further, if the piezoelectric element has multiplepiezoelectric layers and is electrically split so as to be representedas two capacitors 154 a and 154 b, the driver circuit of FIG. 66advantageously requires only a single control signal 150 to drive thepiezoelectric element.

[0392] It has been observed that for a given voltage amplitude of theelectric input signal to the piezoelectric element 22, the electricalcurrent consumption of the piezoelectric element increases sharply forexcitation frequencies just below certain resonance frequencies of thevibration element 26, and drops sharply just above those resonancefrequencies. For rod-like vibration elements 26, these frequenciestypically correspond to longitudinal modes. This electrical effect canbe used to cheaply and quickly determine a particular vibration modewithout using specialized measuring equipment such as a laservibrometer. The sharp decrease in current just above a certain resonancefrequency can be used to reduce the electrical power necessary to drivethe vibratory unit 26 if the motor assembly 20 can be operated at thesefrequencies. Also, the electronics could be configured to automaticallydetect the drop in current and track the frequency at which the dropoccurs, hence advantageously providing feedback. This feedback can beused to adapt the optimal operating frequency to changing externalinfluences, such as temperature and humidity. Also, this kind offeedback can be used to detect the mechanical load that the motor mustmove.

[0393] Specially Configured Piezoelectric Elements

[0394] In some embodiments where the piezoelectric element 22 ispress-fit into the opening 28 in the resonator, the walls defining theopening 28 deform elastically and/or plastically during the press-fitprocess in order to accept the larger piezoelectric element 22 andgenerate the preload. One way to prevent the piezoelectric fromexperiencing sheer forces during the press-fit and to prevent thepiezoelectric from breaking is to put additional metal layers on themechanical contact sides of the piezoelectric. But this time and laborto do so increases costs.

[0395] FIGS. 67-69 show a piezoelectric element 22 with a speciallyshaped end 170 that is configured for press-fitting into recess 28. Theend 170 can eliminate the need for additional metal layers and resultnot only in cost savings, but also in fewer mechanical contact surfacesand therefore in better performance. The new piezoelectric shape canalso generate a more defined contact area.

[0396] The shaped end 170 has at least on one flat 172 adjoining an edgeof the piezoelectric, and preferably two flats 172 on opposing edges ofthe shaped end 170. The interior end of the flat 172 joins an incline ortaper 174 that helps widen the hole 28 that the piezoelectric element 22gets pressed into. The taper 174 joins a flat, central contact area 176.

[0397] The shaped end 170 is advantageously placed on two opposing endsof the piezoelectric element 22, the ends that will abut the wallsdefining the opening 28 and cause the preload on the piezoelectricelement. The flats 172 on opposing ends 170 are spaced a distance apartselected to allow the piezoelectric element 22 to be inserted into anundeformed opening 28. That helps position the piezoelectric. Theinclines 174 make it easier to press the piezoelectric into the opening28. The inclined surface 174 is of sufficient length and inclination toallow insertion without unacceptably damaging the piezoelectric element22. The specific length and inclination angle will vary with theparticular application. The central contact area 176 defines the finaldimension of the opening 28 and sets the preload, it also provides alocalized contact area to reduce the area in driving engagement with theresonator 24 in which the opening 28 is formed. That helps locate thecontact area and axis of engagement and excitation, and it helpsimproves the engagement. Advantageously, the shape of the end 170 issymmetric about central axis 25 so the piezoelectric can be press-fitfrom two directions, but that need not be so.

[0398] The piezoelectric element 22 could be ground after the sinteringprocess that produces the piezoelectric elements, in order to shape thetaper(s) 174 and flat(s) 172. Alternatively, the taper could be producedduring the pressing process by which the piezoelectric elements areformed. The pressing process typically occurs after the layer stackingprocess in the piezoelectric production sequence. In this way noadditional process step is necessary. This method also has an advantageover grinding in that no electrode surfaces are in danger of beingground, resulting in lower piezoelectric efficiency.

[0399] Referring to FIG. 69, the following process is believed suitableto produce this piezoelectric element, although someone skilled in theart can devise other methods given the present disclosure. Thelayer-stacking machine starts with the bottom die and places the firstpiezoelectric layer on top. All other layers follow just as in thenormal lay-up process. Finally the top die is placed onto the stack andthe whole stack is then pressed. During the pressing process, thepiezoelectric elements 22 are forced to accept the shape of the die.

[0400] The die 178 has a shape configured to produce the depictedsurface contour. The die 178 thus has flats 172, inclined surfaces 174,and central flats 176 located so as to form those surfaces on thepressed and sintered piezoelectric elements produced by the die. Thecontours of the die 178 are modified as needed to account for shrinkageand deformation that might occur during formation of the piezoelectricelements.

[0401] The combined surface contour is repeated for as manypiezoelectric elements 22 as are placed in the die. It is important thatthe relative position of the electrodes 180 matches the position of thedie. The stacking machine can ensure proper alignment. The stackedelements are pressed and produce the group of piezoelectric elementsdepicted in FIGS. 67-69.

[0402] Following the pressing process, the piezoelectric elements willbe cut and processed as usual. During the cutting, it may be beneficialto leave the die attached to the stack for stability and alignment. Theresult is a piezoelectric element with said advantages.

[0403] If the piezoelectric is shaped as shown in FIG. 67-68, anadditional advantage arises. Typically the electrodes 180 are printedonto the sides of the piezoelectric element 22. If machines typicallyused to make multilayer capacitors are used, the electrodes 180partially cover the edges of the adjacent sides, and here that includesa portion of the electrode over the recessed flat surface 172. Becausethis surface 172 is sized to fit in the opening 28 without deformationthe slight thickness of the added electrode layer does not affectinstallation. But if that electrode layer 180 were on a normal,square-ended wall of the piezoelectric element being press-fit againstthe walls defining opening 28, then the edges of the piezoelectric wouldbe larger than the center which lacks the electrode layer, and thatwould render a press-fit more difficult. The piezoelectric shape ofFIGS. 67-68 thus eliminates the need for removing the excess electrodematerial.

[0404] It is also possible to shape the die producing the piezoelectricelements such that the deformation that is caused by the polarization ofthe piezoelectric is accounted for. When polarized, the flat contactarea 176 bulges slightly outward, convex to the piezoelectric element22. To offset this polarizing bulge, the die 178 is advantageouslyformed with a slightly convex surface at the contact surface 176 so thatthe resulting piezoelectric element 22 has a slightly concave surface init at the contact surface 176. The amount of curvature is selected sothat after the piezoelectric element 22 is polarized, the contactsurface 176 is flat. The amount of curvature will vary with the specificdesign of the piezoelectric element involved.

[0405]FIG. 75 shows a potential press-fit insertion sequence.Optionally, by first inserting a tapered plug 182 into the opening 28,the insertion edges of the opening 28 are preferably slightlyplastically deformed, which widens portions of the mating edge of theopening. For the illustrated embodiment the end walls 31 engage thepiezoelectric element 22 and place it in compression. To avoidoverstretching and breaking the sidewalls 29 during formation of thetaper, the insertion edges on the end walls 31 can be shapedindividually in two separate steps, or the entire frame can beconstrained against axial deformation.

[0406] When the plug 182 is removed, the piezoelectric element 22 withshaped ends 170 is aligned with the opening 28. The flats 172 preferablyare able to enter the opening 28, with or without the widened edgeproduced by plug 182. The inclined edge formed on the end walls 31defining opening 28 mate with the inclined surface 174 on thepiezoelectric element 22 to provide a sliding insertion to position thepiezoelectric element in the opening 28. The tapered end walls benefit,but are not necessary for the press-fit to occur. They do, however, havethe added benefit of inducing asymmetry in the resonator if so desired.If the sidewalls 29 were to engage the piezoelectric element 22 andapply a compressive force, then an inclined surface could be formed onthe sidewalls 29 or on the corresponding edges of the piezoelectricelement 22.

[0407] The above discussion described the piezoelectric element 22 ascomprising a plurality of piezoelectric layers. This need not be thecase as a single piezoelectric crystal or ceramic block could be formedhaving the specially configured ends 170.

[0408]FIG. 76 shows another advantageous method to press-fit thepiezoelectric element 22 into the opening 28 of resonator 24. To putthis in perspective, a short discussion is given of the objectives, theproblem, and then the solution.

[0409] Repeatability in the performance of the vibratory motors 26requires a consistent preload be applied to the piezoelectric elements22. In order to accommodate variations in the dimension of thepiezoelectric element 22, while achieving the same preload, thesidewalls 29 can be placed in plastic deformation. The slope of thestress-strain-curve is very small in the plastic region, which leads tovery small changes in preload when the length of the piezoelectricelement 22 changes. This allows combinations of shortest piezoelectricelement 22 with the largest opening 28, and the longest piezoelectricelement 22 with the smallest opening 28, to result in essentially thesame preload on the piezoelectric element.

[0410] But when the piezoelectric element 22 is press-fit into theopening 28, it is subjected to frictional forces that lead to high shearforces on the piezoelectric element. Because the piezoelectric materialis brittle, the shear forces can act to delaminate adjacent layers ofthe piezoelectric material. To prevent shear forces from acting on thepiezoelectric the protective plates 34, 84 can be added to take theshear forces. This not only alleviates the stress on the piezoelectricelement 22, but also helps the press-fit as the plates 34, 84 act toguide the piezoelectric into the opening 28.

[0411] To reduce the cost of the vibratory motor 26 and to also improvemechanical coupling between the piezoelectric element 22 and theresonator 24, it is desirable to press-fit the piezoelectric element 22without any protective layers of steel such as plates 34, 84. Thefollowing process allows this by reducing the forces acting on thepiezoelectric during the press-fit operation to a constant and low leveland by making the press-fit process more controllable and thereforeeasier to automate.

[0412] The objective is to have most of the elongation of the sidewalls29 done not by the piezoelectric being forced into the opening 28, butto have the elongation done by another machine. This machine pulls theresonator 24 with force P as shown in FIG. 76 to stretch the sidewalls29. The piezoelectric with tapered edges 82 sits on top of the opening28 in the resonator 24 and is pressed into the opening 28 with a force,F, that is preferably constant, and that is not strong enough to pushthe piezo into the hole by itself. The force F is also not strong enoughto cause damage to the piezoelectric element 22, and is especially notstrong enough to cause shear forces that delaminate the piezoelectricmaterial.

[0413] At some point during the elongation of the sidewalls 29 byincreasing force, P, the piezoelectric 22 starts to slide into the holeunder force, F. By setting the force, F, to a specified value, shearforces between the piezoelectric element 22 and the resonator 24 arelimited to the resulting normal force multiplied by the coefficient offriction. This resulting normal force equals the desired preload forceminus the force, P.

[0414] Once the piezoelectric element 22 starts sliding into the opening28, it is necessary to stop the elongation of the sidewalls 29 by themachine because otherwise the resultant preload on the piezoelectricwill be reduced.

[0415] The pulling machine applying the force P can be controlled by oneof two principles, load control or displacement control. Load controlrefers to controlling the applied load and measuring the resultantdisplacement. Displacement control is just the opposite: controlling thedisplacement and measuring the resultant load. To prevent overstretchingthe sidewalls 29, it is preferable to use displacement control for thisapplication.

[0416] The sidewalls 29 could be curved toward, or away from thelongitudinal axis 25 extending through opening 28. If the sidewalls 29are curved away from the longitudinal axis 25 extending through theopening 28, then by applying opposing forces to opposing sidewalls 29,the end walls 31 can be forced apart, allowing the piezoelectric element22 to be inserted into the opening 28. Upon removal of the forcepressing the curved sidewalls 29 toward each other, the piezoelectricelement 22 is placed in compression. Advantageously, in pressing thecurved sidewalls 29 together in order to enlarge the space between endwalls 31, the sidewalls 29 are stressed beyond their elastic limit so asto achieve the advantages discussed herein.

[0417] Similarly, if the sidewalls 29 are curved toward each other, thenby applying a force to the sidewalls that urges them apart, the endwalls 31 are moved away from each other, allowing the piezoelectricelement 22 to be inserted into the opening 28. Upon removal of the forcepressing the curved sidewalls 29 away from each other, the piezoelectricelement 22 is placed in compression. Advantageously, in pressing thecurved sidewalls 29 apart in order to enlarge the space between endwalls 31, the sidewalls 29 are stressed beyond their elastic limit so asto achieve the advantages discussed herein.

[0418] Instead of tapering the piezoelectric element 22 by applyinginclined surfaces 82 (or 174 (FIGS. 67-69) it is also possible to taperthe edges of the opening 28. It is also possible to have both partstapered. If neither the piezoelectric element 22 nor the opening 28 aretapered, the piezoelectric element 22 starts to slide in at the pointwhere the piezoelectric element and the opening are the same size. Thispresents alignment problems and requires very precise control to avoidoverstretching of the sidewalls 29. Therefore, it is desirable to haveat least one mating part tapered.

[0419] The press-fit method described here is also adaptable to allother press-fits. The vibratory motor 26 with the piezoelectric element22 and the resonator 24 or frame, is used as an example.

[0420] Stepper Motor Approximations

[0421] Referring to FIG. 70, the vibratory element 26 can be operated ata selected excitation frequency that does not coincide with anyfrequency being used for regular operation of the motor assembly 22 andthat therefore does not transport the driven element 42 in a specifieddirection, but rather excites a mode of vibration in the driven element42 itself. This is illustrated in FIG. 70, where the induced mode of arod-shaped driven element 42 has nodes 190. Similar nodes are observedif the driven element is a rotational object such as in FIG. 4.

[0422] In this situation, there is a tendency for the rod 42 to shiftits position so that the contacting portion 44 becomes centered at thenode 190. Depending on what node is closest to the contacting portion44, this results in a forward or backward motion of the rod 42. Thus, byseeking out a specific position along the driven element 42, the motorassembly 22 can provide the incremental movement and locating aspects ofa stepper motor. The step sizes are determined naturally by theparticular mode of vibration that is being excited in the driven element42, and will vary with the mode that is being excited.

[0423] Centering the driven element 42 at known nodes 190 can beexploited to move the driven element 42 into a pre-defined position.This eliminates positioning errors that may have accumulated duringregular operation of the vibration motor 26 and can be used to increasethe accuracy and repeatability of the motor without the need of positionfeedback. This mode of operation requires that the actual position ofthe driven element 42 be within a certain distance to a desired node190, so that the resonant vibration causes movement toward the desirednode.

[0424] The suspension of the driven element 42 affects the frequenciesand node locations of the natural vibration modes of the driven element42. For the purpose of stepping the driven element 42, the influence ofthe suspension must therefore be considered in choosing appropriateexcitation frequencies to achieve this locating activity achieved by thenodes 190. Conversely, the design of the suspension may be influenced bythe need for particular excitation frequency or frequencies and designedto achieve those frequencies. There is thus provided a method andapparatus for using the vibration nodes of the driven object totransport the driven object to a known position for calibration.

[0425] Position Sensing

[0426] There are situations where it is desirable to exactly know theposition of the driven element 42 relative to the vibration element 26.Referring to FIG. 71, an illustrative implementation is described thatuses the characteristic travel duration of a vibration or acoustic pulsefrom the piezoelectric element 22 to monitor the position of the drivenelement. The position of the driven element 42 relative to the vibrationelement 26 can be determined by measuring the time it takes for amechanical vibratory pulse to travel from the vibration element 26 intoand through the driven element 42, and/or vice versa. The vibratorypulse can be generated in the vibration element 26 by the piezoelectricelement 22 or in the driven element 42 by some other generatingmechanisms 198, such as a solenoid, a spring driven impact mechanism, orother mechanical or electronic mechanisms.

[0427] A receiver 196, e.g., a piezoceramic microphone, that is mountedadjacent a distal end of the driven element 42 at a known location onthe driven element can be used to sense the pulse generated by thepiezoelectric element 22, the pulse being sufficient to cause an impactvibration at the selected contacting portion 44. Alternatively, thepiezoelectric element 22 can be used to sense the vibratory pulsegenerated by the generator 198 by exploiting the piezoelectricmaterial's inherent ability to convert a mechanical movement (e.g., ofselected contacting portion 44) back into an electrical signal.

[0428] It is also possible for the piezoelectric element 22 to sense avibratory pulse that it has generated earlier. This requires that thepulse travel through the vibratory element 26 and the driven element 42,be reflected at a location on driven element 42, such as the distal endof the driven element 42, and return to the piezoelectric element 22where it can be sensed. In a similar fashion, by way of reflection, itis possible for a sensor 196 to sense a pulse generated by a generator198.

[0429] The vibratory pulse can be chosen such that its power spectrumdoes not contain significant vibratory energy at frequencies that couldcause the driven element 42 to move. Alternatively, the vibratory pulsecan be incorporated into the operational input signal to thepiezoelectric element 22, for example in form of a brief pause. Becausethe geometries and material properties of the vibratory element 26 andof the driven element 42 are known, and because the position of thecontacting portion 44 on the vibratory element 26 is known, themonitored time difference between pulse generation and sensing isrepresentative of or characteristic of the distance between thepiezoelectric element 22 and the receiver 196 or a distal end of thedriven element 42.

[0430] In some of the various position-sensing embodiments, it isdesirable that the piezoelectric element 22 is temporarily deactivatedprior to the position sensing so that undesirable vibrations are allowedto dampen out. Then the specified signals can be emitted and detected,with the operation of the vibrator element 26 resuming thereafter. It isan advantage of some of these embodiments that, if the piezoelectricelement 22 is used as a sensor as well as actuator, only a singlepiezoelectric element is needed to move the driven element 42 as well asprovide position feedback.

[0431] The pulse generated in either the piezoelectric element 22 or ina generator 198 is reflected at any surface where the mechanicalimpedance changes abruptly. These surfaces include the opposing ends ofthe vibrating element 26 and the opposing ends 200 of the driven element42. Some of these reflections are undesirable and must either be maskedor be otherwise distinguishable from the position-determining pulse.Ways to achieve this include, but are not restricted to, degradingundesired reflected signals by inclining, damping or roughening certainreflecting surfaces such as the distal end 200 b of the driven element42. Given the present disclosure, other ways of altering the ends 200could be devised to allow signals reflected from the ends to bedistinguished for use in the position sensing method and system.

[0432]FIG. 72 shows a different position-sensing embodiment that uses aresistive position measurement method that uses characteristicresistance of a resistive driven object to monitor the position of thedriven object in a way that is analogous to how an integratedpotentiometer operates. The position of the selected contact portionalong the length of driven element 42 varies a resistance that isdetected and used to define a relative position of the elements.

[0433] For illustration, the driven element 42 comprises a cylindricalrod. The driven element 42 is either made of an electrically resistivematerial, or it is made of an electrically insulating material that hasbeen entirely or partially coated with an electrically resistivematerial 204. A carbonated plastic material is believed suitable foreither use. Since the electrical resistance between the selectedcontacting portion 44 of vibratory element 26 and either of the opposingends of the rod 42 depends on the position of the contacting portion 44relative to the rod 42, the position can be determined by measuring theelectrical conductivity, or the electrical resistance, between one ofthe opposing ends of the rod 42 and the vibration element 26.

[0434] The voltage that is necessary for measuring the electricresistance can be small and it can be applied between the vibratingelement 26 and a distal end of the driven element 42. Preferably though,one end of the driven object 42 is connected to a positive supplyvoltage and the other end to a negative supply voltage. By measuring thevoltage at the vibration element 26, e.g., by a voltmeter 204, accurateposition information can be obtained.

[0435] Instead of applying the necessary voltage directly to ends 200 a,200 b of the driven object 42, this voltage can also be applied to thewheels or bearings 46 supporting the driven element 42 provided that thewheels or bearings 46 are made from an electrically conductive materialand that they are electrically insulated from each other and from thevibrating element 26. In such an embodiment, the electrical contactresistance between the bearings 46 and the driven element 26 may have tobe accounted for.

[0436] A suitably coated electrically nonconductive driven object 42 foruse in the described embodiment can be cut from a sufficiently thicksheet of plastic that has previously been dipped into conductive paintand let dry. This forms a conductive layer on the exterior surface ofthe plate. The plate is then cut into strips creating two opposing edgesthat have no conductive layer. Thus, except for the strips or rodsformed from the sheet edges, the cutting process advantageously exposesthe nonconductive plastic on two elongated sides of the driven object(the strips or rods), which results in the conductive paint forming anelongated resistor 202 that wraps around the longitudinal axis of thedriven object. This embodiment can be modified by further removing theconductive layer from one of the ends 200 a, 200 b of the drivenelement. The position can be determined from a measurement of theresistance between the vibration element 26 and one contact point, e.g.,bearing 46 a or 46 b.

[0437] Electrically conductive driven objects 42 can also be used inposition sensing embodiments if appropriate portions of them are firstcoated with an insulating layer and then with an electrically resistivelayer. For example, an insulating layer may be applied to that side of ametallic rod-like driven object 42 that faces the bearings. On top ofthis layer, an electrically resistive layer 202 is applied so that itcontacts the underlying metal only at the ends of rod 42. The positiondependent resistance lies now between a bearing and the end of the rod42.

[0438] Other Variations & Advantages

[0439] In comparison to prior art piezoelectric motors, the presentmotor 26 requires only one piezoelectric element 22 and only oneelectrical excitation to generate motion. Due to the use of resonantvibration modes to generate elliptical motion 100 with a singleexcitation frequency, the piezoelectric element 22 can be smaller thanthose of other bi-directional piezoelectric motors can, and the overallmotor 26 can also be smaller.

[0440] The present invention works very well to provide linear motion ofdriven elements 42. The traditional solution is to use a motor with agearbox driving a rack and pinion arrangement. The present motorassembly 20 provides a simpler arrangement, and less costly arrangementthan prior art motors. Because the selected contacting portion 44engages the driven element 42 by friction, the motor 20 is not damagedif the driven element is externally pushed so as to back-drive themotor. In contrast, such motion would strip the gears of conventionalelectric motors.

[0441] The present invention is especially suited for low costapplications. The simple design can avoid the need for precisionmanufacturing requirements and the attendant cost. It allows low costmanufacturing methods and inexpensive piezoelectric elements. In return,the design provides less power and efficiency than some otherpiezoelectric motors. But the available power and low cost make theembodiments of this invention especially suitable for many traditionalmarkets, such as toys, office equipment, and home automation. Someillustrative examples of the uses for the vibratory motor 26 are givenbelow. But one significant advantage of this motor is its size andsimplicity, which can result in low cost.

[0442] Vibratory motor assemblies 20 are believed possible that are assmall as 0.4×0.4×0.8 inches (1×1×2 cm) in size, moving driven elements42 at 0.5-10 inches per second (1.3-25 cm/sec), with a force of 0.1-3 N.Rotational drive units are believed possible with sizes as small as0.6×0.8×0.8 inches (1.5×2×2 cm) with torques and revolutions per minute(RPMs) depending on the diameter of the rotationally driven object 42.The voltage of the vibratory motor assemblies can be varied depending onthe circuit design and the power needed, but can range from 3V, 6V, 12V,24V 48V, 110V or 220V. Other custom voltages can be used. There is thusa wide range of operating voltages available for the vibratory motors26.

[0443] The size of the vibratory element 26 can be very small, withelements as small as 2×3×10 mm³ believed possible. The cost of thevibratory motors 20 is believed to be half that of competing electricmotors. These motors 26 can produce linear motion, rotary motion, bothlinear and rotational motion, and blocking force when un-powered. Theystart and stop without delay in as little as 0.6 milliseconds, have nobacklash because there are no gears, and can provide fast motion yetalso provide slow motion without using gears. They are inaudible becausethey are driven in the ultrasonic range. The motors require nolubricants and use no toxic substances. They are very accurate and canmove in the micrometer range if needed. By controlling the times duringwhich they are powered, they can achieve various speeds and distances.They generate no magnetic fields, have no brush discharge, and noinductive voltage peaks.

[0444] The advantages of the vibratory motors 26 make them very suitablefor use in CD-ROMs as tray actuators, in scanners to move the light baror rotary elements, in printers and copiers to transport and guidepaper. In home automation applications, the vibratory motors 26 couldactuate air conditioning elements, automatic blinds, lighting controlsand switches, dust protection doors on dust sensitive appliances,automatic locks, or elements in motion detectors. The vibratory motors26 could also be used to position, pan, tilt or zoom remotely operatedcameras, e.g., security cameras.

[0445] The ability to directly engage and drive glass offers advantagesfor using the vibratory motor 26 to control the position and focus ofaccent lighting in homes, retail stores, theaters, galleries, museums,hotels and restaurants. In automotive applications, the vibratory motors26 can be used to position mirrors, headlights and air conditioningvents, and to actuate automatic locks. The stepper-like operation of themotor assembly 20 allows the storing and retrieving of mechanicalsettings, such as mirror position, for each of several drivers under thedirection of a computer.

[0446] The combination of a computer that stores position information inconnection with a positionable motor 20 finds many possibilities insensors that automatically adjust their position. These include opticalsensors, lens cleaning mechanisms for such sensors, protective coversthat open and close by the use of vibratory motors 26, automaticalignment mechanisms, proximity lasers, and adjustments of a variety ofproducts that require movement of small parts by simple motors.

[0447] The vibratory motor 26 is especially useful for toys due toadvantageously low cost, small size and low noise. Dolls could havelimbs moved and eye lids actuated by the motors 26. Remotely controlledvehicles could have steering controlled by the motors 26. Animated toybooks could be provided. Railway models could have moving forks, cranes,signals, railway gates and other actuated components. Various otherapplications of the motor 26 can be made. Further, the vibratory motor26 can be made resistant to liquids, such as water, with appropriatemodifications and coatings, and can provide multiple motions. The lowforce output reduces the possibility of injury. Also, it is possible tomix the electrical operating signal that is supplied to thepiezoelectric element 22 with an electrical signal that contains anon-operational yet audible frequency spectrum. In such an embodiment, apiezoelectric motor 20 can also serve as a simple device for generatingsound and music.

[0448] There is thus advantageously provided a motor assembly 20 thatcosts less to produce than traditional motors of comparable power andspeed. The size and weight of the motor assembly 20 is less, and theinvention allows for exceptional miniaturization of the motor. The motorcan achieve stepper-like motion of the driven elements 42, andpositioning of the driven elements is possible without using positioningsensors on the driven part. The motor assembly 20 allows the use offast, or slow driving speeds, and does not need a gearbox. Because themotor does not use gears, there is no backlash as associated with geartrains. The motor assembly 20 allows the driven element 42 to betranslated, or rotated, or both. The positioning of the driven element42 has positioning accuracy of 1 μm. The operating frequency can beselected to be inaudible to humans so that motor operation is silent.Due to the absence of magnetic fields or spark discharges, the motorassembly 20 and its vibratory element 26 are suitable for use inenvironments that are sensitive to electromagnetic interference orsparks. Quick reaction times of the motor assembly 20 permit controlwith binary state controllers, which are easier to implement and lessexpensive than PID controllers.

[0449] The invention further advantageously provides a vibratory element26 having a piezoelectric driving element 22 and a resonator 24 thatadvantageously holds the driving element 22 in compression. Thisvibratory element combined with a resilient suspension system such asspring 10 can advantageously be provided to users who apply thecomponents to a variety of driven elements at the discretion of theuser. These parts are advantageously designed and configured tocooperate to generate an elliptical path 100 at a selected drivingportion 44 for one or more predetermined applications or for one or moregeneric applications. This combination can be provided as a unit, andcould be provided with or without the spring 50. A user could thus usethese components to drive a variety of driven elements 42.

[0450] Alternatively, a user could be provided with a complete motorassembly 20 containing not only the vibratory element 26 and resilientmount such as spring 50, but also driven elements 42 supported in apredetermined relation to the vibratory element 26. In this alternativesituation, the motor assembly 20 is preferably encased in a housingalong with a suspended driven object 42, as for example a rod for alinear motor. In this alternative situation, the motor assembly 20 anddriven element 42 are ready for installation and use as the user seesfit. The assembly can be used with a driven element used in othermotors, or it could be used as a part of a product configured for usewith the components. Providing the driving elements and suspensionelements allows the user to acquire a low cost driving mechanism havinggreat flexibility in its application.

[0451] The driven object 42 preferably has a smooth and hard surfacelocated to engage the selected driving portion 44. The driven element 42can have a variety of shapes, for example it can be a disc, a rod, awheel, a gear, a beam, a ball, etc, as long as a fairly constant contactforce can be maintained between the selected contact portion 44 and thedriven element 42. This gives designers a wide range of possibleimplementation methods for the motor assembly 20.

[0452] The motor assembly 20 is advantageously encased in a housing toprotect it from dirt and other extraneous contact and potential damage.The housing can be manufactured out of plastic through an injectionmolding process, or made of sheet metal. It is preferably designed suchthat it can be assembled through snap joints. This assembly avoids theuse of more expensive methods including threaded fasteners and is goodfor a fully automated assembly.

[0453] This provides the possibility for the end user to have aninexpensive and small motor unit, which is easy to implement into adesign. In order to increase the flexibility of use, the base 10 or thehousing can have clamping holes or other clamping mechanisms to make iteasier to attach to the end user's product. If the volume of a specificdesigned base 52 or housing is sufficient, the base 52 and/or housingunit could be specially configured to meet the mounting needs of theuser.

[0454] There is thus provided a mechanism and method for generating anellipse 100 that has a first semi-axis and a second semi-axis, with thelength of the first semi-axis being useful to generate a difference infriction force between the selected contact portion 44 and an engagingsurface of a driven element 42, during the motion components in thedirection or directions of travel along the elliptical path 100. Thiselliptical motion is advantageously provided by a single excitationfrequency provided to a piezoelectric element 22 that results in atleast two vibrational modes generating the elliptical path 100. Thiselliptical motion 100 is achieved by exciting at least two vibrationalmodes at least one of which, and preferably both of which, are not purelongitudinal or pure bending modes, and superimposing those modes togenerate the elliptical motion at the selected contacting portion. Thiselliptical motion 100 is advantageously achieved without having to placethe selected contacting portion 44 into contact with any driven element42.

[0455] The practical result of having modes other than purelylongitudinal and purely bending, is that the major axis defining theelliptical path 100 of the selected contacting portion 44 is angledrelative to the longitudinal axis 25 of the vibratory element 26. Themajor and minor axes of the elliptical path 100 are not aligned with thelongitudinal axis 25 of the resonator as is common with prior artvibratory devices. The angle of the major axis of the elliptical path100 relative to longitudinal axis 25 is advantageously not near 0degrees or multiples of 90 degrees. For ease of description, the anglewill be described relative to the orientation of parts in FIG. 1 in thefirst quadrant, but one skilled in the art will appreciate that theparts can be rotated through other quadrants or that the orientation ofparts can be changed—without altering the relative angles discussedhere.

[0456] Because the greatest motion and fastest rate of travel isachieved when the longitudinal axis of the elliptical path 100 isaligned with the travel path of the driven element 42, the vibratoryelement 26 is preferably angled relative to the driven element 42 inorder to align those axes. If the major axis of the elliptical path 100aligns with the longitudinal axis of the driven element 42, then thisabove-discussed angle can be considered to be the angle α, discussedabove. The perfect alignment of the major axis of the elliptical path100 with the longitudinal axis of the driven element 42 is oftencompromised for practical reasons.

[0457] Because the elliptical motion 100 is angled relative to thelongitudinal axis 25 of the resonator 24, elliptical motions with largeaspect ratios can be used. Ratios of the major to minor axes of theelliptical path 100 are advantageously over 5, more advantageously over10, and preferably over 20 to 1. But when the semi-axis becomes toosmall, the selected contacting portion may not adequately disengage fromthe driven element when the ellipse is aligned with the driven elementand thus ratios of 30:1 or more are difficult to achieve, especially atlow cost. Further, as the ratios increase, the performance approachesthat of an impact drive vibrator element. Thus, ratios of over 150:1,and even 30:1 are difficult to achieve and use. While most useful sizedelliptical paths 100 are believed to have aspect ratios of about 3:1 to150:1, preferably the ratios are from about 4:1 to 30:1, and ideallyfrom about 5:1 to 15:1. If aspect ratios are used up to and over 150:1,then the resulting applications find use primarily in impact drive typesof devices.

[0458] The amplitudes needed to achieve elliptical path 100 at theselected contacting portion 44 are preferably obtained by largemagnification of small input signals. That requires selecting orcreating resonance modes of vibration sufficiently close to the selectedinput signal to achieve a usable amplitude. Advantageously, for eachvolt input to the piezoelectric element 22, the selected contactingportion 44 can achieve 0.3-0.5 microns of motion along the major axis ofthe elliptical path 100. Preferably, for each volt input, the motionalong the major axis of the elliptical path 100 is 1 micrometer orgreater. These motions are the result of resonant vibration modeamplifications that increase the motion by factors of at least 100, andtypically by factors of 1000 or more.

[0459] It is possible, but less desirable, to use a small resonancemagnification and instead provide a larger input signal in order toachieve the needed amplitude to generate an acceptable elliptical path100 at the selected contacting portion 44. If one of the vibration modesthat results in the usable elliptical path 100 is off-resonance, thenthe electric input signal to the piezoelectric element 22 can beincreased sufficiently to result in a usable elliptical motion, onesufficient to moves the driven element 42. Thus, it is believed suitablein some applications to have one volt input to the piezoelectric element22 result in motion along the major axis of the elliptical path of 20-50nanometers, but with movements of 100 nanometers or more beingdesirable.

[0460] Thus, the selected contacting portion 44 moves in a firstelliptical path having a major axis and minor axis when the vibrationsource, such as piezoelectric element 22 is excited by a firstelectrical signal that causes at least two vibration modes that aresuperimposed to create the first elliptical path 100. Preferably, atleast one of the vibration modes is other than a pure longitudinal modeand other than a pure bending mode. When at least one of the twovibration modes is off-resonance, the first electrical signal isamplified sufficiently to cause the at least one off-resonance vibrationmode to produce a motion of the selected contacting portion 44 havingsufficient amplitude that the resulting elliptical path 100 can move thedriven element 42 during use. As used here, the reference to anoff-resonance vibration mode refers to a vibration mode that issufficiently away from the resonance mode that the resulting motion doesnot generate a usable elliptical motion, motion insufficient to drivethe driven element 42.

[0461] The desired elliptical motion 100 is advantageously achievedwithout requiring the selected contacting portion 44 to engage thedriven element 42. Depending on the angle of engagement, reflected byangle α, the engagement can cause impact or bending that may affect theelliptical path 100 or the resulting motion of the driven element 42,and appropriate compensation can be made for those effects.

[0462] As mentioned above, the generation of the elliptical path 100 atthe selected contacting portion is most easily determined in a localizedcoordinate system that does not align with the longitudinal axis 25 ofthe vibratory element 26. A coordinate transformation to align themotion so that one axis of the elliptical path 100 aligns with thevibratory element 26 or preferably with the driven element 42 allows thepractical use of the elliptical path 100 to be evaluated.

[0463] If multiple motions of a driven element 42 are desired to beproduced from a single vibratory element 26, then the selectedelliptical path 100 is likely to be a compromise among several potentialelliptical paths at various frequencies, and if desired, at severalselected contacting portions 44. If multiple motions are desired to beproduced by a single piezoelectric element 22, it is preferable that thefrequency used to achieve the different elliptical motions besufficiently different to clearly separate the frequencies and theirresulting motions. The frequencies for the separate motions arepreferably separated by at least the same margin as the frequency rangeover which the substantially uniform elliptical motion 100 is achieved.Thus, for example, if a first elliptical motion 100 is achieved over afrequency range of 2.5 kHz on either side of a first frequency, for atotal range of 5 kHz, then the second frequency is advantageously atleast 5 kHz from the first frequency, and preferably more.

[0464] Ideally, the major axis of the elliptical path 100 is alignedwith the axis along which the driven part 42 moves. As shown in FIG. 1,that alignment angle corresponds to the angle α between the longitudinalaxis 25 of the vibratory element 26 and the axis 45 of a rod-like drivenelement 42. This alignment may be achievable if the driven element 42 ismoved in only one direction. But when the same vibratory element 26 isused to move the driven element 42 in opposing directions, relativealignment is difficult or impossible to achieve, especially in bothdirections. Further, the alignment considerations for bi-directionalmotion as discussed below is advantageously used even when only a singledirection of motion of the driven element 42 is used.

[0465]FIG. 81 will be used to illustrate the considerations in thisalignment. FIG. 81 illustrates a first elliptical path 100 a having amajor axis e_(x1) for moving the driven element 42 in a first direction,and a second elliptical path 100 b having a major axis e_(x2) for movingthe driven element in a second, opposing direction. The major axise_(x1) is inclined at an angle β₁ relative to axis 45 of the drivenelement 42 and the major axis e_(x2) is inclined at an angle β₂ relativeto that axis 45. The axis 45 can be viewed as parallel to a tangent tothe driven element 42 in the direction of motion of the driven element42 at the selected contacting portion 44. The motion along the firstdirection, the motion resulting from ellipse 100 a is believed totypically be the easiest to achieve and will typically have the majoraxis e_(x1) of ellipse 100 a most closely aligned with the axis 45 ofthe driven element 42, while the major axis e_(x2) is not as closelyaligned with that axis 45. Thus, β₁ is typically smaller than β₂ when β₁is selected first. But that need not always be the case as the ultimateselection of elliptical paths 100 a, 100 b is a result of compromisingseveral factors as discussed herein.

[0466] While it is ideal for β₁ and β₂ to be 0, so that the major orminor axes of the elliptical paths 100 to align as closely as possiblewith the desired motion of the driven element 42, that is difficult toachieve for multi-direction motion. For bi-directional motion where thesame motion is desired but in different directions, it is believed thatβ₁ and β₂ will range from 5 to 40 degrees with respect to a tangent tothe driven element 42, along the direction of motion of the drivenelement 42, at the selected contacting portion 44. It is believedpossible, but less desirable to have the angles go from 40 to 45degrees. It is very desirable to have the angles β₁ and β₂ perfectlyalign the major axis of the elliptical paths 100 a, 100 b with thedirection of motion of the driven element, and preferably align themwithin 0 to 5 degrees. As used herein, because the orientation of partscan increment the angles through various multiples of 90 degreesrelative to a horizontal axis, the angles given should be construed asrelative angles rather than as absolute numbers. Thus, for example, thereference to aligning the major axes and the driven path within 0 to 5degrees includes angles on opposing sides of the horizontal X-axis asshown in the drawings. That thus includes an absolute angle of 360-365degrees relative to a common axis of measurement.

[0467] As shown in FIG. 81 the angle is relative to the axis 45 of thetranslating rod 42. But the driven element 42 could comprise a rotatingdisk (e.g., FIG. 4). Usable but sometimes undesirable performance isbelieved to be achieved if β₁ and β₂ range from about 5 to 85 degreesfrom the tangent to the driven element at the location of the selectedcontacting portion 44. Preferred performance levels are believed to beachieved if β₁ and β₂ range from about 5-35 degrees and 55-85 degrees,and the best performance is believed to be achieved when β₁ and β₂ rangefrom about 15 to 25 degrees and 65 degrees to 75 degrees.

[0468] As stated or implied above, because of symmetry considerationsrelative to the 0 and 90 degree axes, the above range can vary in 90degree increments in absolute value relative to a common axis of origin.The above discussions and angle ranges are believed to apply tomulti-direction motion.

[0469] In order to achieve the desired angles β₁ and β₂, it is believedthat the angle α should be maintained within the previously discussedranges. The particular combination of β₁ and β₂ that is used istypically chosen so that the major axis of elliptical paths 100 alignsas close as possible with the axis of the driven element 42. The closerthe alignment, the more efficient the transfer of motion from thevibratory element 26 to the driven element 42 along the selected axis ofmotion 45.

[0470] But from the various angles discussed, it can be observed thatthe selected vibration mode(s) of the resonator 24 that result in usablevibratory motions along elliptical paths 100 orientated at angles β₁ andβ₂, are neither purely longitudinal nor purely bending modes. Thus, inproducing the elliptical motion 100 at the selected contacting portion44, the angles β₁ and/or β₂ are such that the major and minor axes ofthe elliptical paths 100 a, 100 b do not align with the longitudinalaxis of resonator 24 of the vibratory element 26. Further, the angles β₁and/or β₂ are such that the major and minor axes of the elliptical paths100 a, 100 b do not align with a pure bending mode of that vibratoryelement 26, e.g., along axes 38, 40 in FIG. 1. The angle ∞ between thedriving element such as vibrating element 26 and the driven element 42is varied in order to allow the advantageous alignment of the major andminor axes with the direction of motion desired for the driven element42.

[0471] This also means that the vibrational modes of the vibratoryelement 26 that generate elliptical paths 100 a, 100 b at the selectedcontacting portion 44, have at least one vibration mode that is not apurely longitudinal vibration mode along axis 25, and not a pure bendingmode (e.g., along the axes 38, 40 for the configuration depicted in FIG.1). Thus, for example, the two vibration modes being selected togenerate elliptical path 100 a preferably do not include a purelongitudinal or pure bending mode of the resonator 24 in order toproduce the first elliptical motion 100 a of the selected contactingportion 44, and the same is true with the vibration modes to generatethe second elliptical path 100 b. If a pure longitudinal or pure bendingmode is used to generate the first elliptical path 100 a, then thevibration modes used for the second elliptical path 100 b do notnecessarily include a pure longitudinal or pure bending mode of theresonator 24 in order to produce the elliptical path 100 b. Further, ifa vibration mode is used that includes a pure longitudinal vibrationmode along axis 25, then desirably the axis 25 is inclined to the drivenelement 42 at an angle α that is other than 0 and 90 degrees ormultiples thereof, and that is preferably between about 5-85 degrees andmultiples thereof.

[0472] As the angles β₁ and β₂ become greater relative to the drivenelement 42, the contact results in greater impact between the selectedcontacting portion 44 and the driven element 42. When the aspect ratioof one or both elliptical paths 100 a, 100 b becomes large, so that oneaxis is much larger than the other axis, the contact approaches that ofan impact drive. It is believed possible to have one of the ellipticalpaths 100 a, 100 b have a high aspect ratio, sufficiently high that theresulting motion can effectively be considered an impact drive, and havethe other elliptical path with a lower aspect ratio to produce anon-impact drive. Advantageously, aspect ratios of the elliptical paths100 that produce a pure impact type drive, are avoided.

[0473] Further, it is believed possible that the teachings of thisdisclosure can be used to configure a vibratory element 26 having veryhigh aspect ratio elliptical motions 100 a, 100 b in opposingdirections. When the aspect ratio of the major to minor elliptical axesbecome great enough, the particular direction of motion around theelliptical path is not determinative of the direction in which thedriven element moves. Instead, the angle of inclination β of the majoraxis relative to the driven element becomes the determinative factor indeciding the direction of motion. Thus, it is believed possible to usetwo high aspect ratio elliptical paths 100 a, 100 b, at the same (ordifferent) selected contacting portions 44, to create an impact drivemoving the driven element 42 in the same direction. Indeed, theprinciples of this disclosure could be used to have a singlepiezoelectric element 24 generate two longitudinal resonance modes attwo different frequencies, each of which is used in an impact drive.

[0474] Whether high aspect elliptical motion is used to approximate pureimpact drive, or whether a pure linear motion is achieved to implementan impact drive, the motion of the driven element 42 can be achieved attwo separate frequencies. But the use of two frequencies can result indifferent rates of travel of the driven element. The differences in therate of travel by using different frequencies can be enhanced if a highaspect elliptical motion is used in which the direction of travel of theellipse (e.g., clockwise v counter-clockwise) changes, or in which theangle β, changes. Further, the teachings herein can be used even if morethan a single piezoelectric element 22 is used to cause the multiplefrequencies for the impact-type motion or to cause actual impact motionusing mainly longitudinal resonance of the vibratory element 26.

[0475] It is desirable to have the angles β₁ and β₂ be reasonablyconstant over as wide a range of excitation frequencies to vibratorydriving element 22, as possible. For example, if any excitationfrequency signal to piezoelectric element 22 over a 2 kHz range resultsin elliptical motion 100 at the selected contacting portion where theangle β₁ does not vary by more than 5 degrees, then it becomes easier todesign the vibratory system, and it becomes easier to allow the use ofcomponents with larger tolerances in performance parameters. It isdesirable to have the angles β₁ or β₂ vary less than 10 degrees, andpreferably less than 5 degrees, and ideally less than 3 degrees, over aslarge range of excitation frequencies as possible. This allows the angleα of inclination between the predominant axis 25 of the vibratingelement 26 and the motion axis 45 of the driven element 42 to be setwith reasonable tolerances, and to use components with tolerancesobtainable at affordable prices, and produce acceptable motion. Thisespecially allows the use of low cost motors in a wide variety ofcommercial applications, as discussed herein.

[0476] It is thus desirable to have the selected contacting portion 44move in approximately the same elliptical path 100 when the frequency ofthe driving signal input to the piezoelectric element 22 varies by aslittle as 200 Hz on either side of the selected frequency.Advantageously, approximately the same elliptical path 100 is achievedwhen the frequency of the driving signal varies as much as 2.5 kHz, ormore, from the selected frequency. It is thus desirable that theexcitation frequency to the source of vibration 22 can vary by as muchas 2.5 kHz on either side of the selected frequency, and preferablygreater, while still producing suitable amplitudes for elliptical paths100 at the inclination angles β₁ and β₂. In relative terms, it isdesirable to have a range of 5-10% of the selected excitation frequencyachieve suitable elliptical paths 100, with the inclination angles β₁and β₂ varying less than 25 degrees, and preferably less than 10degrees, and ideally by about 5 degrees or less, over that frequencyrange. The ability to do so will vary with the particular designcriteria and performance requirements.

[0477] One way to help maintain the inclination angles β₁ and β₂reasonably constant over a reasonably wide range of excitationfrequencies is to vary the various design parameters of the motor asdiscussed herein. The above discussed angles of 25 degrees, preferably10 degrees and ideally about 5 degrees or less are each considered to bereasonably constant, with angles of about 5 degrees or less being themost preferred and most reasonably constant. Maintaining theseinclination angles reasonably constant is most easily achieved by havingthe effect of the relative phase change on the angles β₁ and β₂compensate for the effect of the amplitude change on the angle. Toachieve this it is useful to select a set of vibration modes that havesuitable directions of motion and frequency response curves for phaseand amplitude. Further, using a coordinate transformation to view andanalyze the elliptical motion 100 in a localized orientation also makesthe design easier.

[0478] As used herein, the predominant axis is used to indicate an angleof inclination between the vibratory element 26 and the elliptical path100 of the selected contacting portion 44. The predominant axis willvary with the geometry and shape of the vibratory element 26, and thelocation and orientation of the selected contacting portion 44 on thevibratory element 26. For elongated vibratory elements 26 with theselected contacting portion 44 located at a distal end, as in FIG. 1,the predominant axis is likely to be the longitudinal axis 25, or anaxis orthogonal thereto, or a rotation about such axes. For non-straightvibratory elements 26 as shown in FIG. 77, with the selected contactingportion 44 located on a distal end, the predominant axis is the axis 25through the distal end, or an axis orthogonal thereto, or a rotationabout such axes. For selected contacting portions 44 n located along thelength or on intermediate portions of vibratory elements 26 as shown inFIG. 6, the predominant axis is again the longitudinal axis through thedistal end 36 a, or an axis orthogonal thereto, or a rotation about suchaxes. The particular predominant axis will vary in part with the motionof the selected contacting portion 44 and an adjacent axis of thevibratory element 26 that can be readily used for orientating thevibratory element to achieve alignment of the elliptical path 100 at theselected contacting portion 44 with the driven element 42.

[0479] To test the quality of a motor 20 after it has been assembled, itis advantageous and cost-effective to measure a few electromechanicalcharacteristics of the motor using its piezoelectric element 22. Thecharacteristics include, but are not limited to, the current that isdrawn by the piezoelectric element 22 for a predetermined input signal,and the electrical signal that is generated by the piezoelectric elementwhen it is turned off after having appropriately excited vibrations inthe vibration element 26. It is also possible to track thesecharacteristics during the lifetime of a motor 20, and in doing so tomonitor motor efficiency without the need of special equipment such as alaser vibrometer.

[0480] The above disclosure focuses on using a single electrical signalto excite a single piezoelectric element 22 to produce an ellipticalmotion 100 at the selected contacting portion 44 that is inclined to thepredominant driving axis (e.g., longitudinal axis 25) of the resonator24. That elliptical motion 100 is an unrestrained motion of the selectedcontacting portion 44 and occurs whether or not the contacting portion44 engages the driven element 42. But that inclined elliptical motion100 can be produced by using more than a single piezoelectric element 22on the resonator 24. This invention thus has broader applicability tovibratory elements 26 that use plural piezoelectric elements 22 toachieve the elliptical motion 100 inclined to predominant driving axis(e.g., the longitudinal axis 25) of the resonator 24. Thus, for example,as shown in FIG. 81, first and second piezoelectric elements 22 a, 22 bcould be on different portions or sides of resonator 26 (or contactingdifferently located walls defining one or more openings 28 in theresonator 26 as in FIG. 2), in order to produce an inclined ellipticalmotion 100 a at the selected contacting portion 44. A thirdpiezoelectric element 22 c could be on yet another portion of theresonator in order to produce a different elliptical motion 100 b at theselected contacting portion 44. This use of multiple piezoelectricelements 22 a-22 c requires more complex electronics and thus hasdisadvantages, and it may limit the applicability of some aspects of thepresent disclosure. But it illustrates that some aspects of thisdisclosure have applicability beyond use with the single piezoelectricelement 22 as described herein.

[0481] The above description is given by way of example, and notlimitation. Given the above disclosure, one skilled in the art coulddevise variations that are within the scope and spirit of the invention.Further, the various features of this invention can be used alone, or invarying combinations with each other and are not intended to be limitedto the specific combination described herein. Thus, the invention is notto be limited by the illustrated embodiments but is to be defined by thefollowing claims when read in the broadest reasonable manner to preservethe validity of the claims

What is claimed:
 1. A vibratory apparatus for moving a driven element,comprising: a vibration source that converts electrical energy directlyinto physical motion, and a resonator having an opening defined by atleast two opposing sidewalls which are stressed beyond their elasticlimit to hold the vibration element in compression, the vibration sourcebeing within that opening so that the vibration element is held incompression by the resonator under a defined preload, the vibrationsource causing the resonator to vibrate in at least a first mode tocause a selected contacting portion on the resonator to move in apredetermined manner.
 2. The apparatus of claim 1, wherein the vibrationsource is press-fit into the opening.
 3. The apparatus of claim 2,wherein the vibratory element is a piezoelectric element.
 4. Theapparatus of claim 2, wherein the at least two sidewalls are curved. 5.The apparatus of claim 3, wherein the at least two sidewalls are curved.6. The apparatus of claim 3, wherein the piezoelectric element has atleast two opposing edges that are inclined and located to engage edgesof the opening to make it easier to press-fit the piezoelectric elementinto the opening while reducing damage to the piezoelectric element. 7.The apparatus of claim 5, wherein the piezoelectric element has at leasttwo opposing edges that are inclined and located to engage edges of theopening to make it easier to press-fit the piezoelectric element intothe opening while reducing damage to the piezoelectric element.
 8. Theapparatus of claim 3, wherein the piezoelectric element has at least twoopposing edges that have surfaces substantially parallel to the abuttingwalls defining the opening, and an inclined surface extending therefromto a contacting surface abutting one of the walls, the contactingsurface exerting the preload on the piezoelectric element to place thepiezoelectric element in compression.
 9. The apparatus of claim 3,wherein the opening in the resonator is defined by at least two opposingedges that are inclined and located to make it easier to press-fit thepiezoelectric element into the opening.
 10. The apparatus of claim 5,wherein the opening in the resonator is defined by at least two opposingedges that are inclined and located to make it easier to press-fit thepiezoelectric element into the opening.
 11. The apparatus of claim 3,further comprising a resilient support element for supporting theapparatus, the support element being interposed between thepiezoelectric element and a portion of the resonator opening.
 12. Theapparatus of claim 5, further comprising a resilient support element forsupporting the apparatus, the support element being interposed betweenthe piezoelectric element and a portion of the resonator opening. 13.The apparatus of claim 3, wherein the first mode is excited by a firstelectrical signal applied to the piezoelectric element that results inthe selected contacting portion moving in an elliptical motion ofsufficient amplitude to move a driven element in a first direction whenthe apparatus is engaged with the driven element during use of theapparatus.
 14. The apparatus of claim 13, wherein the resonator isexcited by a second electrical signal applied to the piezoelectricelement that results in the selected contacting portion moving in asecond elliptical motion of sufficient amplitude to move a drivenelement in a second direction when the apparatus is engaged with thedriven element during use of the apparatus.
 15. The apparatus of claim5, wherein the resonator is excited by a second electrical signalapplied to the piezoelectric element that results in the selectedcontacting portion moving in a second elliptical motion of sufficientamplitude to move a driven element in a second direction when theapparatus is engaged with the driven element during use of theapparatus.
 16. The apparatus of claim 3, wherein the selected contactingportion is resiliently placed in contact with a driven element that isconstrained to move in a predetermined manner and caused to move by thefirst elliptical motion.
 17. The apparatus of claim 13, wherein theselected contacting portion is resiliently placed in contact with asurface on the driven element that is constrained to move in apredetermined manner and caused to move by the selected contactingportion engaging the surface.
 18. The apparatus of claim 2, furthercomprising a second resonator having a second opening defined by atleast two opposing sidewalls which are stressed beyond their elasticlimit, and a second vibration source that converts electrical energydirectly into physical motion, the second vibration source beingpress-fit within that second opening so the second resonator holds thesecond vibration source in compression under a defined preload, thevibration source being placed in a position to cause the secondresonator to vibrate in at least a first resonant mode to cause aselected contacting portion on the second resonator to move in apredetermined manner, the first and second resonators being arranged sothe selected contacting portion of each resonator drivingly engages thesame driven element.
 19. A piezoelectric apparatus for moving a drivenelement, comprising: a resonator having a longitudinal axis with anopening partially defined by two sidewalls on opposing sides of thelongitudinal axis and two opposing end walls on the longitudinal axis, apiezoelectric element held in compression by the opposing end walls,each of the sidewalls being stressed beyond its elastic limit to holdthe piezoelectric element in compression, the resonator having aselected contacting portion which moves in a first elliptical motionwhen the piezoelectric element is excited by a first electrical signal.20. The piezoelectric apparatus of claim 19, wherein the sidewalls arecurved.
 21. The piezoelectric apparatus of claim 19, wherein at leastone of the end walls or two opposing sides of the piezoelectric elementthat engage the end walls have edges that are inclined to facilitatepress-fitting the piezoelectric element into the opening and wherein thepiezoelectric element is press-fit between the end walls.
 22. Thepiezoelectric apparatus of claim 19, wherein at least one of thesidewalls is curved so it bows away from the piezoelectric element. 23.The piezoelectric apparatus of claim 19, wherein at least one of thesidewalls is curved so it bows toward the piezoelectric element.
 24. Thepiezoelectric element of claim 19, wherein a portion of an elasticelement for supporting the resonator is interposed between one of theend walls and the piezoelectric element.
 25. A method of placing apiezoelectric element in compression in a resonator, the resonatorhaving end walls and sidewalls defining an opening sized to receive andplace the piezoelectric element in compression, comprising: increasingthe distance between opposing end walls enough to allow thepiezoelectric element to be forced between the end walls with a forcethat by itself could not force the piezoelectric element between the endwalls in the original state of the opening, and thereby placing thepiezoelectric element in compression while also stressing the sidewallsbeyond their elastic limit.
 26. The method of claim 25, furthercomprising providing an inclined surface on at least one of either theend walls or the corresponding edges of the piezoelectric element, andforcing the piezoelectric element into the opening by engaging said atleast one inclined surface.
 27. The method of claim 25, comprisingpulling the opposing end walls apart while forcing the piezoelectricelement into the opening.
 28. The method of claim 25, wherein thesidewalls are curved.
 29. The method of claim 26, wherein the sidewallsare curved.
 30. The method of claim 25 wherein the sidewalls are curvedaway from each other, and comprising urging the opposing, curvedsidewalls toward each other in order to move the end walls away fromeach other and then placing the piezoelectric element between the endwalls.
 31. The method of claim 25 wherein the sidewalls are curvedtoward each other, and comprising urging the opposing, curved sidewallsaway from each other in order to move the end walls away from each otherand then forcing the piezoelectric element between the end walls. 32.The method of claim 25, comprising interposing a resilient mount for thepiezoelectric element between the piezoelectric element and one of theend walls.
 33. The method of claim 26, comprising interposing aresilient mount for the piezoelectric element between the piezoelectricelement and one of the end walls.
 34. The method of claim 25, whereinthe resonator has a longitudinal axis passing through the opening withthe sidewalls being on opposing sides of that axis and the end walls onthe longitudinal axis.
 35. A piezoelectric element configured to bepress-fit into an opening in a resonator, the opening being defined bysidewalls located on opposing sides of a longitudinal axis through theopening and separated by a first dimension, and opposing end wallslocated on the longitudinal axis and separated by a second dimension,comprising: a piezoelectric element having a first dimension that issmaller than the first dimension of the opening and having a seconddimension larger than the second dimension of the opening and selectedto stress the sidewalls beyond their elastic limit when thepiezoelectric element is inserted into the opening, the piezoelectricelement having inclined edges corresponding in location to edges of theend walls when the piezoelectric element is aligned to be inserted intothe opening.
 36. The piezoelectric element of claim 35, wherein thesidewalls are curved toward or away from the piezoelectric element. 37.A piezoelectric element configured to be press-fit into an opening in aresonator, the opening being defined by sidewalls located on opposingsides of a longitudinal axis through the opening and separated by afirst dimension, and opposing end walls located on the longitudinal axiswith a resilient support for the resonator being interposed between oneend wall and the piezoelectric element during use, the contacting endwall and the contacting surface of the resilient support being separatedby a second dimension, comprising: a piezoelectric element having afirst dimension smaller than the first dimension of the opening andhaving a second dimension larger than the second dimension of theopening and selected to stress the sidewalls beyond their elastic limitwhen the piezoelectric element is inserted into the opening with theresilient support interposed between the piezoelectric element and oneend wall, the piezoelectric element having at least one inclined edgecorresponding in location to at least the edge of the end wall when thepiezoelectric element is aligned to be inserted into the opening. 38.The piezoelectric element of claim 37, wherein the sidewalls are curvedtoward or away from the piezoelectric element when that element isinserted into the opening.
 39. A piezoelectric element configured to bepress-fit into an opening in a resonator, the opening being defined bysidewalls located on opposing sides of a longitudinal axis through theopening and separated by a first dimension, and opposing end wallslocated on the longitudinal axis with a resilient support for theresonator being interposed between one end wall and the piezoelectricelement during use, the end walls being separated by a second dimension,wherein the piezoelectric element has edges on surfaces that are locatedto engage walls defining the opening, with the edges having inclinedsurfaces on them to make it easier to press-fit the piezoelectricelement into the opening.
 40. A resonator for use with a piezoelectricactuator, the resonator having a continuous walled, externallyaccessible opening sized to receive a piezoelectric element and hold theelement in compression, the opening being defined in part by opposingsidewalls that are curved.
 41. The resonator of claim 40, wherein thesidewalls are curved away from the opening.
 42. The resonator of claim40, wherein the curved sidewalls have a uniform cross section for asubstantial portion of the length of the sidewall.
 43. The resonator ofclaim 40, wherein the curved sidewalls have a rectangular cross section.44. The resonator of claim 40, wherein the opening comprises opposingend walls on a longitudinal axis of the opening, the sidewalls being onopposing sides of the longitudinal axis.
 45. The resonator of claim 40,further comprising a piezoelectric element located in the opening, thepiezoelectric element being sized relative to the opening to stress thesidewalls past their elastic limit.
 46. The resonator of claim 40,further comprising a resilient support element interposed between, andheld by compression between, the piezoelectric element and one walldefining the opening.